What does it mean if someone says “Did you party animals go out?hahaha”?

It means "did you go to a party on New Year's?" The hahahaha after implies the sender was being sarcastic, implying they know you didn't go out because you have a young child.

"go out" just means to go places outside of your home. In this context, probably bars or night clubs for alcoholic drinks. Party Animals are just people known to go to parties with lots of people and alcohol frequently and usually drink too much and stuff like that. So I assume this may have just been a sarcastic joking comment if that's not the type of people you usually are.

party animal is an idiom that just means a person who enjoys partying and does it regularly.  if you have a small child the texter may have been saying it in a spirit of sympathetic sarcasm.