While in the womb, i.e. when the sex is uncertain, you can use "it". Once the sex is determined, the mother and father would be offended if they heard you call their baby "it" BUT, I've heard people say "it" before so... It is curly - describes an object, his/her hair curly - can be used to describe the baby's hair It's name is Rex - acceptable for a pet His name is Rex - acceptable for a baby

No, you are right. It is for things. To call someone's baby 'it' is insulting, like saying the baby is an animal.

If you mean "baby animal." The puppy is so small. It's cute. It has curly hair. But for people, generally we use he/she/they. Now, for pet owners. He/she/it is allowed. Max is my dog. It's big and furry. Rover is her dog. He is cute and cuddly.