I was just goofing around seeing if there is any way to drop a baby, and I found if you click outside of the inventory GUI to drop the baby, it makes the baby disappear and you get the "don't drop the baby" message, but never get the baby back in your inventory.

It is probably intentional. Babies if they get dropped in real life will probably die. That's just a guess I have never tried it so I won't know XD

Closed as feature is intentional