How old are they? We have always made a small pen for them, in the bigger pen or right next to it. That way they get used to each other but the babies are still safe.
Some people say to keep them in there for three weeks before you introduce them. They also suggest putting them in the big coop at night, next to the others, and when they wake up together they are OK. I would still want to be up early and out there before they got up to watch over them.
I was free ranging mine when I introduced them. I put them in my little pen, and they were fine. The little ones could run right in and out because the wire was to big, (they can squeeze through such tiny places!) but the big ones diddnt even act like they saw them.
Than last week I penned the whole flock up, since I am putting in my garden. The big ones started picking on the babies, so I had to keep them seperate again. They seem to do a lot better when they don't have to be in compitition for space, then the big ones see the babies as a threat.
In any case, i would not leave them unattended for several days, untill you can trust them. Take them out, watch them, and bring them back in when you have to leave them. And make sure the little ones have a refuge, somewhere they can get away from the big flock.
