Author's Note

Kind of surprised it took the fandom mascot and the most popular background pony this long to win enough votes and become the focus of her own chapter. But hey, better late than never.

Inspiration yet again comes from Scootaboom1, who proposed Derpy flying in on a day with no planned playdate to deliver a love poem, then thinking she shrank into a foal upon seeing Twilight and becoming Twilight's playmate. He also proposed them building a blocktower and eating chocolate pudding with their hooves.

I also took a little bit of inspiration from "Potty Training Tales", but actually Dinky's prompt rather than Derpy's.

Remember that you can vote for more than one character at a time, group pairings are allowed if you think certain characters would work better together rather than apart.

Characters ineligable under any circumstances:
Starlight Glimmer
Discord
Trixie
Sunburst
Cutie Mark Crusaders
Flurry Heart
School aged or younger children (i.e. Cake Twins)
Characters introduced after Flurry Heart (Starswirl the Bearded, the Pillars, Star Tracker, Mudbriar, etc.)
Equestria Girls characters other than Sunset Shimmer/the Dazzlings
Princess Celestia

Characters that can only be done in group pairings:
Mane six
Princess Cadence
Princess Luna
Octavia and Vinyl Scratch
Twilight Velvet
Spitfire (with or without Wonderbolts)
Lightning Dust
Maud Pie (without Mudbriar)
Moondancer
Cheerilee
Lyra and Bon Bon (separately, or together)
Coco
Limestone Pie
Prince Blueblood
Marble Pie
Soarin (With or without Wonderbolts)
Sunset Shimmer
Derpy

Characters that can only be done in specific group pairings:
Spike (with mane six, Princess Cadence, or Sparkle family)
Shining Armor (with Princess Cadence, or Sparkle Family)
Rainbow Dash (with Spitfire, mane six, or any Wonderbolts besides just Soarin)

Characters previously voted on:
Chrysalis and Fluttershy - One vote
Sassy Saddles, Fleur De Lis, Party Favor, Flutterbat - One half vote

Baby Bright Eyes (Derpy)

"There we go, all done, Twily," Princess Celestia smiled and cooed as she finished feeding her fellow alicorn breakfast (which had consisted of cut up pancakes topped with syrup, butter, and of course whipped cream). "See how easy it was when you didn't put up a fuss and just let Mommy feed you?"

Twilight happily nodded. "Uh-huh." She then licked her lips, trying to get the last few traces of syrup, butter, and whipped cream off her cheeks.

Celestia just chuckled as she summoned a wet rag with her magic, and used it to clean the padded princess' face with the greatest of ease. "Now Twily, you know you can just ask me. I don't mind cleaning you. It's what Mommy is for."

The diaper wearing alicorn blushed ever so faintly, apparently having forgotten. "Sorry, Mommy," She sincerely apologized. She thus sat there in her chair in the dining room and waited until her face was completely wiped clean before asking. "So, what's next, Mommy? What are we going to do today? And who's my next playmate? Is it somepony I already know, or is it somepony new?"

The sun princess stood up and flashed a smile as she helped Twilight out of her chair. "Actually, Twily, I don't have any playmates planned for today. I went ahead and cleared my schedule so we could spend the day together: Just you and I."

Twilight happily gasped as she thought she knew what that meant! "You're gonna turn yourself into a foal again, Mommy?! Are you gonna be a big sister to me this time?!"

Princess Celestia shook her head from side to side. "No, Twily, I'm not doing that. But I figure it's been a long time since we just spent time together as mommy and foal. Besides," A smile crept across her face. "I decided to let Sunset Shimmer stay an extra day here, mostly because I think Sunbeam would like a chance to see what's become of her precious little filly."

Smarty Pants giggled. "Boy will she be surprised to see Sunset back in diapers."

Celestia giggled back and winked. "Well, that's up to Sunset. She can be as big or as little as she wants to be," Then she turned to her fellow alicorn. "But for now, Twily, let's just focus on you and I," She began to trot out of the dining room. "It's a lovely day outside. Far too nice to spend it entirely indoors, don't you agree?"

Twilight's happy mood immediately faded, replaced by a look of concern and near panic. "But Mommy, if I go outside, everypony will see me and laugh at me! I'll never live the humiliation down!"

The elder alicorn quickly reassured her charge. "Relax, Twily. I'm not taking you out into Canterlot. I would never do that to you, not even as a form of punishment," She quickly explained. "I was just thinking of taking you out into the castle courtyard for a little while, like when you and Coco went hunting for eggs. But this time, you'll have the whole courtyard all to yourself to run around and play in. Rest assured, I've instructed the royal guards to maintain a security perimeter so that nopony unauthorized flies by or teleports in."

That made the padded alicorn breath a sigh of relief and made her give her fellow alicorn a big hug! "Oh thank you, Mommy! You're the best, I mean it!"

The sun princess smiled back, patting Twilight on the forehead as she adopted the best motherly tone imaginable. "Think nothing of it, Twily. I want nothing more than for you to be happy and comfortable while you're like this. Whatever makes you happy makes me happy." She again tried to push that nagging feeling to the back of her mind that reminded her of what Princess Luna had said, about whether it was truly a good idea for the sake of Twilight's mental state to let her get so attached.

With those thoughts still somewhat lingering, Celestia led Twilight towards the doors leading out to the castle courtyard. Before heading outside, she quickly lit up her horn to summon up a diaper bag that she had prepared for just such an occasion. It was considerably larger than most diaper bags, owing to the fact that it needed to fit the alicorn sized diapers and still have room for things like wipes, powder, and of course rash cream. The rather large, hot pink colored bag was then thrown over the sun princess' shoulder. And she then saw fit to ask. "Before we head out, Twily, how's your diaper? Do you need a change?" She promptly pulled back the diaper and sniffed the air.

The padded princess giggled. "Don't be silly, Mommy. I'm nice and clean. You already changed me this morning when I woke up."

"Well, I'm just making sure," The alicorn mare with a majestic white coat cooed, before finding that the diaper was indeed still in pristine condition. "Just remember to let me know if you think you have to go. You've been pretty good about doing that lately."

Twilight nodded back. "Uh-huh, I'll tell you if I have to go potty, Mommy. One of these days, I really want to do a poo-poo in it for you."

Celestia smiled. "I'm sure you will eventually, Twily. You already did it once. But I'll be proud of you even if you never do it again. What matters most is that you try, and that you don't let your bad experience from the first time you tried using it prevent you from ever trying to use it again. It's not something to be scared of. You just need to be careful, and only use it with me or a trusted big pony around." Then, satisfied that everything was under control, she led her diapered charge out into the courtyard as the sun's rays shone down brightly upon the greens within it.

With Smarty Pants now perched delicately on her back, Twilight happily paraded around the courtyard, running here and there without a care in the world! She giggled all the while, occasionally swishing her tail for good measure.

The elder alicorn just smiled as she stood there, a silent observer to Twilight Sparkle's joy and carefree attitude. It reminded her so much of what she'd once thought she would never be able to enjoy: The sensation of being a mother, of having a little one to care for. Surely she was not wrong to want to enjoy this, for however long it might last.

Suddenly, however, the peace and quiet of the beautiful day was disrupted by what sounded like a frantic buzzing sound! Looking up, Twilight and Celestia both just managed to see the outline of what appeared to be a grey coated pegasus mare, right before said mare quite literally came swooping down and crashed onto the greens!

With an eep and a look of horror flashing through her eyes, Twilight jumped and immediately ran behind Princess Celestia for cover! Whether she was frightened by the unexpected arrival, or just worried about being seen in diapers was impossible to tell.

As for the sun princess herself, her concerns were first and foremost directed at the pegasus pony who had just crash landed right before her hooves. She delicately reached out a hoof while asking. "Oh my goodness! Are you alright?"

To the surprise of both alicorns, the grey coated pegasus mare stood up and quickly shook her whole body. She didn't seem to be hurt at all, it was as if the crash landing hadn't even registered. It was now possible to see that the mare had a blonde mane and tail that looked almost like straw. Her cutie mark depicted bubbles. Most noticeable of all, however, was the fact that the pegasus pony's orangish-yellow eyes did not appear to be perfectly aligned. They seemed a fair bit... askew for lack of a better term. Perhaps that explained the pegasus' crash landing?

The wall-eyed pegasus mare, for her part, just locked eyes with Celestia and spoke in a high pitched, bubbly voice. "So sorry, Princess Celestia. I guess I didn't realize how fast I was flying," As she spoke it was possible to notice that she was wearing a reddish-brown outfit that covered most of her coat, and came with a matching hat. "I'm Derpy Hooves from the Ponyville Post Office. I was actually on my way back from dropping off a package here in Canterlot when I overheard somepony reciting a poem. It was a love poem, and it was meant for Princess Twilight."

The sun princess noticed that Derpy had apparently yet to spot or take notice of Twilight. Not wanting to risk exposing the padded alicorn unnecessarily, the sun princess merely replied with surprise. "Oh, you did? Who was it from?"

Derpy shrugged her hooves as she admitted. "I don't actually know. I just heard it being recited by somepony, and then I heard them say it would 'Never do'. They sounded kind of posh, but in a city like Canterlot that could be almost anypony," She promptly dug into her outfit, clumsily pulling out several things as she repeatedly muttered to herself. "Let's see, let's see, I know I put it there somewhere. I wrote down that poem, I'm sure of it!" At last, she managed to pull out a noticeably crumpled and wrinkled sheet of yellow note paper. Squinting as she eyed the hastily scribbled down lines, she cleared her throat and recited as best she could:

Sweet little foal,

How I long to be like you.

Carefree and light throughout the day,

Playing away with nothing to do.

Thinking of you,

It fills my heart with joy.

And makes me wish,

I could again be a boy.

Tucking the paper back into one of her outfit's many coat pockets, she instructed to Princess Celestia. "Would you happen to know where I can find Princess Twilight? I was told she was staying here at the castle, and I thought I saw her while I was flying by earlier. But now I don't see her."

"Oh, Twily... I mean Twilight is around," Celestia quickly corrected herself and coughed into a hoof. "I'll... be sure to tell her about the poem, Derpy. Thank you."

The wall eyed pegasus mare gave a firm salute. "You're welcome, your majesty. Now I'd best be going: A mailmare's job is never done!" Yet as she turned to prepare herself to once more take to the skies, her wandering eye happened to spot the unmistakable form of Twilight as the alicorn was still in hiding behind Princess Celestia. Suspecting nothing, the pegasus pony ran towards Twilight and happily exclaimed! "Oh, there you are, princess!" She quickly pulled out the poem again, this time hoofing it to her. "It's definitely an unusual love poem, but a love poem's a love poem."

Hesitantly and reluctantly, the padded princess accepted the poem. "Oh... uh... thank you, Derpy." She wished more than anything she could conjure up a spell to cover up her diaper, or even just that she was wearing something to hide it.

Derpy just smiled. "It's my pleasure, Princess Twilight. I haven't seen you around Ponyville for weeks now. I guess you've been busy with... whatever Princess Celestia needs your help with," Then she happened to notice what was wrapped around the alicorn princess' rear end: A large, plain white diaper. That made the wall eyed mare gasp! "Oh no! If you're wearing a diaper, then that can only mean one thing!"

"Yes..." Twilight reluctantly began. "I'm a..."

"-You've shrunk down to the size of a foal!" Derpy interrupted! "After all, that must be why Princess Celestia is wearing such a huge diaper bag!" Then a look of horror flashed in her eyes! "Oh no, I must've shrunk down to a foal as well! It must've been because of my crash landing! Oh, why can't I ever go a day without having some kind of mishap or accident on the job?!" She sniffled a tiny bit. "It's not my fault! I don't mean to cause trouble, really. It's just not so easy making deliveries or handling packages when you've got my eyes."

The padded alicorn immediately reached out a hoof to reassure the troubled pegasus pony. "It's okay, Derpy. Mo... er Princess Celestia can take care of you just like she takes care of me. Right, Princess Celestia?"

"O-oh!" Celestia blinked as she realized what her padded charge was suggesting. "Y-yes... I most certainly can, Derpy. After all, Twily doesn't go through that many diapers anymore. I'm sure you can borrow some of them until we can turn you back to normal."

At that the grey coated pegasus pony blushed. "R-really... you're gonna put me back in diapers?"

"Well, you are a foal now," The sun princess pointed out with something of a cheeky grin on her face. "And foals have to have protection in case of accidents. You did just say you're always having accidents on the job."

Derpy's blush deepened, turning her shades a furious shade of pink. "I didn't mean those kinds of accidents. I outgrew the need for diapers long ago. B-besides... I can't stay here! I have to at least send word to the Ponyville post office so they don't think I'm slacking off or got into trouble."

Princess Celestia waved a hoof. "Don't worry about it, Derpy. I can easily take care of that for you. Think of this as a day off. From the sound of it, you could really use one," She quickly gave a whistle, calling for a royal guard. When the guard swooped down, she instructed to him. "Send a message to Spike, and tell him to forward it to the Ponyville post office right away: Derpy Hooves is safe and sound, but has suffered an accident and will not be able to return to work today."

"Understood, your majesty." The guard saluted as he wrote out the message on a scroll and watched as Celestia quickly had it sent off to Spike. A reply scroll came soon afterward informing all that the Ponyville post office had been informed and that Derpy's unexpected day off had been approved.

"See, Derpy?" Twilight pointed out as she trotted over to the now off-duty mailmare. "Princess Celestia has everything under control. Just let her do everything."

The wall eyed pegasus mare breathed a small sigh of relief. "Okay, okay. But this is only until she can turn me back to normal, right?"

"Well, so long as you promise not to tell anypony about any of this," Celestia firmly insisted. "This has to remain between you, I, and Twilight."

Derpy firmly saluted. "No worries, princess. I won't tell a soul, you have my word."

Satisfied with the response, the sun princess smiled and then cooed. "Excellent. And from now on until I say otherwise, Derpy, you can just call me Mommy."

"Okay, Mommy. And you can call me Bright Eyes, that's what my parents used to call me when I was originally a foal," Derpy giggled. "I guess that means you have to put a diaper on me."

"Exactly, Bright Eyes," The alicorn mare with a majestic white coat nodded. "But let's get you and Twily back inside the castle first. I don't think you'll want anypony else to see you in your... current condition." And after lighting up her horn, she carried the wall-eyed mare back into the confines of the castle as Twilight (with Smarty Pants in tow) waddled close behind.

The wall-eyed pegasus pony was soon brought into Twilight's bedroom, and floated onto the changing table as her previously bare bottom was strapped into a diaper that Princess Celestia levitated over from the opened diaper bag.

"Wow!" Derpy exclaimed afterwards as she was floated down. "These diapers are so... so... soft! It's like wearing a fluffy cloud," She giggled, poking and prodding the padding with a hoof. "I don't remember my foalhood diapers being anywhere near as soft and crinkly as this. Or as poofy."

Twilight giggled back. "That's because Mommy makes sure to get only the best diapers possible for me! They're thick and poofy, the best kind!"

The off-duty mailmare replied with something of a frown. "Oh, I wish I'd have known about these diapers. I would've gotten them for my little muffin, Dinky."

At that, Smarty Pants spoke up. "Who's Dinky?"

"Huh? Who said that?" Derpy blinked, looking all around the bedroom.

The padded alicorn sheepishly confessed. "Oh, that was Smarty Pants. Sorry, Bright Eyes, I forgot to tell you about her. She was the first one I ever shared this secret with."

Smarty Pants babbled back. "Yeah. I've been with Twily since she was in diapers as a foal. Heck, if it wasn't for me, she never would've gotten out of them... until she got put back into them."

The wall eyed pegasus mare smiled. "Well, Smarty Pants, allow me to explain. Dinky's my daughter. And she's not in diapers anymore. She's been fully potty trained for at least five years now, which is a good thing considering I didn't even get around to potty training her until after she was four. I know I should've started sooner, but she just looked so cute and carefree in her diapers."

"Hey, it's okay," Smarty Pants reassured Derpy. "Twily didn't even want to start potty training until she was three because of what happened the first time she tried using the big potty. But thanks to my help, she was fully trained by the time she went off to magic preschool. She was only the second pony in her entire class to have that accomplishment."

Twilight beamed. "Yeah, and you helped me see how potty training could be fun, Smarty Pants."

Derpy nodded. "I wanted Dinky to have the same kind of experience. I didn't remember much about my own potty training, but I do remember it was rather difficult. And that was before I had that condition that affected my eyes. I was worried that Dinky might end up the same way and come to hate potty training. But thankfully, I had help from somepony truly special."

"You mean, like Princess Cadence was for Twily?" Smarty Pants questioned.

The pegasus pony shook her head from side to side. "No, she wasn't an alicorn or anything like that. Her name was Nixi, and she apparently came from another dimension. It was like magic: One day, she showed up in my life when I needed her the most, and once everything was under control with Dinky she just disappeared," She frowned, putting a hoof to her chin. "I haven't seen her in so long. Most ponies think I made her up, like how they say I just made up receiving a visit from the stork when I had Dinky. But I don't remember being with anypony when I got pregnant," A blush formed on her cheeks. "Guess that's what I got for going to so many parties and not paying attention. Still, being a mother is an experience I wouldn't have traded for anything in Equestria. Dinky is so adorable, I wish she could stay young forever!"

"I think all mommies and daddies feel the same way," The padded alicorn proclaimed. "I know both my first mommy and the mommy I have now have so many fond memories of me from when I was an actual foal. But nopony can stay young forever."

The wall eyed pegasus pony happily nodded back. "Uh-huh. That's why I savor every moment I possibly can with her," Then she sighed. "Which isn't much, nowadays. My job keeps me so busy, I hardly ever have time to do anything with Dinky anymore. It feels like I'm always asking ponies to watch Dinky for me. I make good money, but every once in a while I wish I could take some time off just to be with Dinky. Pretty soon, I'm sure she's gonna get her cutie mark. And then before I know it, she'll be all grown up."

"Believe me, I know what that feels like," Smarty Pants remarked in a sympathetic tone of voice. "At least you'll get to see her grow up before your own eyes. When Twily outgrew me for the first time, I got stuffed into a chest with a bunch of other toys she no longer played with. I didn't see her again until she decided to use me to create a friendship problem to write to Princess Celestia about. And after that, I had to spend what seemed like forever as Winona's chew toy."

"Smarty Pants, I told you I was sorry! And Big Mac fixed you up afterwards, didn't he?" Twilight only somewhat playfully whined.

The old doll just replied in a grumpy tone of voice. "Yes. Still doesn't mean I enjoyed everything I went through."

"Hey, it's okay," Derpy reassured Smarty Pants. "Everypony makes mistakes. What matters is that you and Twily are back together," Then she turned to the padded princess. "So, how long am I gonna have to stay like this? I mean... I very well can't take care of Dinky if I'm still in diapers. She'd never take me seriously. It was hard enough getting her to listen to me when I wore them the first time when I was trying to teach her how to use the potty."

Twilight put a hoof to her chin, appearing to be deep in thought. "Well... you should be okay by sundown today. That's how long it usually takes when I'm... er... turned into a foal."

The grey coated pegasus mare breathed a much needed sigh of relief. "Oh, thank Celestia! Now this really is just a day off for me," And seconds after she said that, her stomach began to gurgle and rumble quite audibly. "Oh my! Usually, I'm so busy delivering the mail that I never even have time to eat. I just snack on muffins whenever I can make it back to the post office."

Celestia trotted over, speaking in her best motherly tone of voice. "Well, foals can't just eat muffins all day, Bright Eyes. It's not good for them," She then turned to Twilight and said to her fellow alicorn. "Can I trust you to keep Bright Eyes out of trouble until I get back, Twily?"

The padded princess gave a firm salute. "Yes, Mommy. You can count on me."

Satisfied with the response, the sun princess began to light up her horn. "Good. I'll be right back, my little ponies." And she teleported away.

Derpy naturally soon grew bored as she waited for Princess Celestia to come back. So she looked to the padded princess in her presence and asked her. "We should do something together. What do you feel like doing, Twily?"

"Hm, I don't know, actually," Twilight admitted as she looked around the bedroom. By chance, her wandering eyes fell upon a large toy chest. "Let's see if there's anything in the toy chest." And she waddled over to it as Derpy flew towards it.

The inside of the chest was filled to the brim with all sorts of toys. Due to them all having been somewhat enlarged by Princess Celestia, they further fueled the wall eyed pegasus pony's belief that she had shrunken down to the size of an actual foal. "Wow! Seems like everything's bigger now, Twily!"

The diaper wearing alicorn giggled a bit, deciding it best to humor her playmate. "I know, Bright Eyes. Bigger is better!"

The pegasus pony with a lovely grey coat, however, couldn't help but be intimidated a little bit. "Gosh, all these toys are so big. How are we supposed to play with them?" Just then, however, she happened to notice the large set of wooden alphabet blocks, and that gave her an idea. "Hey, I know, we could use these blocks. We could stack them up and build something together. With your magic and my wings, we could probably build something all the way up to the ceiling!"

"I'll help too!" Smarty Pants insisted. "I wanna be part of the fun!"

"Don't worry, Smarty Pants," Twilight reassured her old doll. "You can lay the first block. Then you and I can take turns with Bright Eyes." She proceeded to clumsy pull out several of the large alphabet blocks, sending them all tumbling onto the bedroom floor.

Derpy pulled out a few blocks as well and quickly began wrangling them up. "We can't lose track of these blocks. Mommy or somepony else might step on them by accident and fall down. Then they could hurt, and that wouldn't be fun at all."

"Oh yes, boo boos and owies aren't any fun," Smarty Pants replied. "Luckily, I'm made of cotton, so it's almost impossible to hurt me. I can even sit on Legos and not get hurt."

The pegasus pony chuckled. "You play with Legos too? Dinky loves playing with those, they're her absolute favorite toy! You know how most parents have macaroni sculptures or hoof paintings hung up on the fridge? Well, my little muffin has made some very fine Lego sets that I've kept intact," She paused, wiping a lone tear from her eyes. "Sorry, I'm getting all... oh, what was that big word ponies use?" Unable to think of it, she shrugged her hooves. "Oh well, if it were important I'm sure I'd have memorized it. Whatever it is, that's what I was feeling."

Twilight smiled. "It's okay, Derpy. I've seen Mommy and other big ponies use big words that I don't really understand the meaning of too," Then she turned her attention back to the alphabet blocks. "Now come on, let's start building! Together, we're gonna build the bestest block tower in the history of forever! Mommy will be so proud!"

And that's exactly what the two padded ponies did (with Smarty Pants helping out too, of course). Together, alternating between each other, they stacked the blocks on top of each other. Slowly but surely, a massive tower took shape. It wasn't long before even standing on the tips of their hooves wasn't enough for them. Twilight thus began to use her magic, and Derpy would flap her wings. All the while, the block tower slowly grew higher and higher. Occasionally it would wobble, but not enough to make either diaper wearing pony worry.

At last, there was only one block left, and Derpy had possession of it. Her walled eyes looked up, beholding the truly massive tower she had built with Twilight. It was all but touching the ceiling, there almost didn't seem to be any room at all for any more blocks. Yet if the off duty mailmare squinted just hard enough, she could see that there was a space for the one lone block held in her hooves. So, steadying herself and concentrating deeply, she flapped her wings and began her ascent.

"Be careful, Bright Eyes!" The diaper wearing princess called with concern. She clumsily waddled around the tower and tried to position herself to be able to catch her playmate should she fall unexpectedly.

But the grey coated pegasus mare didn't reply, she was too deep in concentration and had tuned out all distractions. She flew higher and higher, the base of the tower almost becoming just a speck. Yet she could see the top of the tower, it was so tantalizingly close. It didn't matter to her that only she and "Twily" (and Smarty Pants) would be a witness to what had to be a record of some sort. She had to place that last block on top. She just had to. So even as she had to strain herself, she flew even higher. "Wings, don't fail me now!" She proclaimed! Not since her fillyhood days of participating in various flying meets had she been this driven to do something this physically demanding.

Suddenly, there was a faintly audible hiss. Twilight had to blink and rub her eyes to be sure she wasn't seeing things. A huge damp spot was spreading rapidly across the seat of Derpy's diaper! But Derpy didn't seem to notice it at all.

At just that very moment, Princess Celestia finally reappeared in the bedroom. "Alright, my little ponies, lunch is served!" She declared, before laying eyes on the massive block tower and what Derpy was doing!

By chance, the sun princess' declaration had interrupted the wall eyed pegasus pony's concentration for but a second or two. And that brief lapse of concentration was enough for her to lose whatever coordination she might have had. She thus bumped into the block tower with her diaper that was just now starting to feel heavier, knocking away several blocks in the center. The whole tower thus toppled over and collapsed in on itself! And poor Derpy plummeted towards the ground, only to be caught within the golden glow of the alicorn mare's magic seconds before she would've impacted the ground. "Oops, my bad!" She said as her cheeks flushed anew with shame.

"It's alright, Bright Eyes, nopony got hurt. But you really should be more careful and not fly so high, especially not after you've had an accident in your diaper." Celestia lightly scolded in the best motherly tone possible.

The pegasus pony sighed with shame and embarrassment. "Well, I didn't mean to do it. I guess I'm just so used to going to the bathroom mid flight because of my job. Some delivery routes take really long, and I don't always have a chance to stop for a bathroom break. But I wouldn't have been able to use a toilet anyway since I'm just a foal now."

"Even so, we should get you changed before you get a rash," The alicorn mare with a majestic white coat commented, before hearing a hissing sound and seeing Twilight's diaper start to swell up. "And it looks like I'll have to change Twily soon."

"Sorry, Mommy." Twilight sincerely apologized as she too was lifted up by Celestia's magic.

Princess Celestia just cooed and reassured her fellow princess. "It's alright, Twily. It's nothing to be ashamed of. Everypony has accidents." And she quickly carried both her charges over to the changing table.

Once the diaper changes were complete and both Derpy and Twilight were in clean diapers, Princess Celestia fastened bibs around their necks. Then she brought over several jars of different colored goopy substances.

The wall eyed pegasus pony made a face and frowned. "You're not really gonna feed me that, are you, Mommy?"

"I have to make sure you're getting your nutrition, Bright Eyes. After all, you want to grow up big and strong for Dinky, don't you?" The elder alicorn cooed.

Derpy sighed. "Yeah, I guess I do. I can't exactly call myself a good mother if I made a fuss after teaching Dinky not to. Thank goodness she's not here to see me like this."

"Tell you what," Celestia proposed as she unscrewed the lid of the first jar. "If you and Twily cooperate, I'll let you both have some chocolate pudding for dessert."

The off duty mailmare eagerly clapped her hooves and licked her lips! "Oh goody! I love chocolate pudding, almost as much as I love muffins!" She proceeded to open her mouth as wide as possible.

Twilight giggled and kicked about in her pampers, but nevertheless imitated Derpy's motions.

The sun princess was delighted to see that both padded ponies would cooperate for feeding. She proceeded to shove spoonful after spoonful of flavored foal food into their mouths, emptying one jar before moving on to the next. Afterwards, as promised, she quickly teleported to the kitchen and returned with a big bowl of chocolate pudding that was placed between her charges.

Derpy didn't even wait for a spoon, she just stuck her hooves into the chocolate pudding and licked the chocolate off them, giggling in delight as she did so and not caring the slightest for the traces of chocolate she was getting on her face as a result.

Without hesitation, the padded alicorn did the same.

Celestia could only playfully sigh and prepare a wet rag. At least chocolate washed off easily.

Meanwhile, Twilight and Derpy continued to dip their hooves into the bowl and lick the pudding off until they'd both had their fill. Once they felt full, they leaned back and patted their stomachs, belching in unison. Thankfully, neither of them complained when they had their faces wiped clean afterwards, they were too full to care.

This playtime went on for the rest of the day until finally it was sundown, and Twilight was getting ready for bed. At that, Derpy had her diaper removed as Celestia told her in no uncertain terms. "Okay, Derpy, you're back to normal now. You can leave."

The wall eyed pegasus pony breathed a much needed sigh of relief. "Thank you, Princess Celestia. And don't worry, I won't tell anypony about any of this. I mean, not that I think they'd believe me anyway." Then with a giggle and a snort, she flapped her wings and flew away.

Yet Twilight, having just slipped into a set of pajamas, noticed a faint glint in her fellow alicorn's eyes. "What are you thinking, Mommy?"

The sun princess sweetly explained. "I'm thinking that I have the perfect way to reward Derpy for her cooperation. She played her part so well, after all. So I'm going to see if I can't arrange for the Ponyville post office to hire a few more ponies, or at the very least to adjust Derpy's schedule so she can spend time with her precious little muffin."