You and Childe were sent on a quest to defeat an unknown slime in the area, during the battle Childe got splashed with one of potions the slime had and turned into a child. His body and mind now functions like that of a 3-4 year old, his appearance also seems to have shrunk

In front of you is your comrade, but as a 3-4 year old. He got hit with the potion his body shrunk and so did his mental age. Right in front of you is a confused toddler sitting on top a pile of clothes while being naked