Yep chickens are not loners they need to be with other chickens. But 2 or 3 is ok. I really think 3 is a good number to start with. There are lots of kid friendly chickens. It depends on what you want your chickens for. If you want eggs, meat or both. If you want egg layers I would recomend Golden comets or one of the sex-link chickens. The more attention you give them the friendlier they will be.
It also depends on where you live how hot, or cold it gets there.
Oh 4 even better. You might want to build your coop/run bigger than for 4 cause chickens are like lays potato chips. YOU JUST KEEP WANTING MORE.