Even at that age a kid can have small horns, which while not sharp or able to stab can to damage because they are hard. Also the heads alone are designed as a natural battering RAM. Doesn't matter how small they are they can hurt, especially if the baby is practically the same size as the kid.
My neighbor has 2 very sweet goats. Super fuzzy and friendly. They got out and have been at my house since thanksgiving. I love them, I'm always petting them, and giving them cookies. They're my goats now. -.-
The goat is literally assaulting a child