I was able to separate my babies from the older girls with a split coop for several months. My hubby put up chicken a chicken wire wall so they could see each other but not physically interact. Integration took a long time for me, but I think it was because of my inexperience....I want everyone to get along NOW !
The 2 groups could see each other and I did not mix them until after the babies were close to the same size. When I did I placed my big girls, one hour after dark into the babies area, then woke up early and let them all out.
I did this for about a week. Because they were used to the split coop, the big girls would roost in their own area.....so I moved them to the other area until I took down the wire separation. The wire separation came down the week one of the pullets laid an egg...then they took to the nesting boxes very quickly.
Because they free range during the day when I am home everyone was able to interact with lots of room to run away if things got out of hand. I worried and fretted a lot....again, perhaps my inexperience.
I did have one BR that absoultely went out of her way to attack the young ones with an aggression I had never seen before. First time ever I took one of my hens to the feed store...she just wouldn't stop. Now, everyone gets
along well, and the integration is complete.
I hope this helps you. Bottom line, separate areas where they can see each other for awhile worked for me. Place them together after dark. Similiar size is important too I think.
Anne