When I put chicks in the coop with the older birds I make sure they have plenty of places they can hide to get away from the bullies. This fall I had to wait a little longer until I sent the young turkeys to freezer camp because they tolerate no new comers. Mean things!Depends on the chickens. Sometimes I can get away with it, sometimes I can't. I usually wait to introduce them when they are half the size of the adults, and before that, all thats separates them is a dog kennel panel so that they can see each other and interact. When you first introduce them, they'll get picked on. You'll probably see chickens bonking them on the head. You need to decide the violence level, if it gets to bad, then separate again. If the chicks are avoiding the older chickens and it's just a peck here and there, they'll be fine. The older chickens need to establish a pecking order, so you won't get out of that one. The chicks will figure out their place pretty fast and eventually everyone will get used to each other. As they grow, they'll be considered higher on the pecking order.
If a broody hen hatches, I have found that everyone is accepted right away as hers, and if the other chickens try to peck at them, momma hen will protect her babies. My rooster even helped raise them.
Good Luck.
My four week olds still have a heat lamp and I'm in PHOENIX!
Yesterday we had a record high temp (tied) at 82 degrees!
I'm putting some four day olds with a broody mama into a grow out pen without a heal lamp though.
Wow, if I did that my poor babies would be panting! Of course your 4 week olds probably aren't fully feathered yet. Mine were hatched by a broody in an outdoor rabbit coop with temps ranging from 15 - 60 over the past 6 weeks. They did amazingly well and feathered out really fast. I was surprised how little time they spent under mama. I won't do that with my incubator hatched chicks though, they'll be inside until feathered out.