While the Antidote did helped Twilight feel better from her Spring fever, it caused a side effect transforming her to a baby. Her friends decide to have Zecora make another antidote but it leaves Spike in a situation to keep Twilight occupied. Especially he never took care of babies before.

Thanks to Psalty123 for editing this one shot.
https://www.fimfiction.net/user/297899/Psalty123