"Kid" is very informal. You'll want to use "child" unless you are speaking with friends. ("Kid" isn't rude, it is just informal.) "Baby" is more conversational than "infant". For instance, if you are talking to someone, it is more natural to say "What a lovely baby" than "What a lovely infant". One example of when to use "infant" is when describing things, such as when shopping: "Where can I find infant clothes."

The noun "Kid" is an informal synonym of "Child." It is also a young goat. The noun "Infant" refers to a baby that has not yet learned to walk.

I would say "kid" and "child" are the same thing. "Infant" and "baby" are also almost the same, although perhaps an infant is more of a very small baby (a newborn baby). You can use baby for an older baby or toddler, as well as a newborn or very young baby.

Thanks for the answer :)

"Child" is used in a formal/polite situation. --"The child has the flu." "Kid" is used in a more casual setting. --"This kid aced his test." Use "Kids" when talking about more than one. "Infant" would be a formal referral to a young child. --"I have experience babysitting infants" "Baby" would be used in a casual or familiar setting. --"What a cute baby!"