I have three sets of chickens from March, May and June and they're finally all in the run and coop together. I kept the youngest chicks in the a clear plastic box which I took out into the yard. Then I let some of the older chickens out and approach the box. Then, let the chicks out while the older ones were kept in the run. Then let a couple of the older chickens out with the chicks. Then, kept the brooder box in the coop but so that the older chickens couldn't get them. Then, let them all outside together. Finally, all in the coop together, all the time. I think I did that over 1.5 to 2 weeks. There were, of course, still some feathers lost, but they all seem to keep together based on age. Some of the youngest chicks, presumably roos, actually go after the older chickens. I also always kept separate feeders and waterers for them.