I mix my pullets with my flock as soon as they are feathered and off the heat lamp. I do it slowly though. First I let them get to know each other for a few days to a week but still keep the babies separated from the big girls. (they can see each other but not peck each other since I separate them either using a cage or a fence). After that I open the cage door so the babies can get in and out and away from the big girls if they are being pecked. After a few days they get used to each other and everything is peaceful. I still would feed them grow mash (the big girls will eat it too so I offer it in several separate bowls so that they don't fight over it) and layer feed for the big girls. I hope that helps. I usually don't have any problem when I do it this way.