I have a mixed flock with many different ages and breeds of chickens.........As soon as new chicks are fully feathered and off the heat lamp, usually 4-8 weeks depending on the breed, they get moved to the outside coop (large hoop house/tractor) and either stay in the back 1/2 of the coop divided by heavy deer netting or if only a few, in a large wire dog kennel for a week or two (the original flock can see them and get used to them) before letting them loose with the flock, supervised the first time. I have done this many times with many different breeds and have had no issues. I have had issues trying to introduce fully grown birds into the flock, the hens have eventually worked things out but not the roos, never an issues with the youngsters. My coop is fairly large, and the birds get to free range year round all daylight hours on 10 acres so the main flock leaves the coop for most of the day and the new youngsters usually don't venture out for at least a week or two so the big ones are not around much to hassle them. Hope this helps, this is just what has worked for me in my situation.