Looking for a magical girl anime episode where the heroine is turned into a baby
I know a manga (which has an anime too) where a girl turned herself as a baby, but had difficulty to change back due to the "baby language", but the purpose was not for talking with another baby but for being a replacement until the actual baby is back.

The manga is Hime-chan no Ribbon, in the books, this event happened in a bonus chapter of the volume 9.