There are a couple things you can do. First you can add a wire cage that sits within the run of the older chickens so they can see each other without getting hurt. The second thing you can do is introduce them to the current older flock when you are giving treats or something that they love. You just need to use something that is a distraction so the new babies being introduced aren't the main show. You need a headliner. Mine love grass even more than the scratch so when I introduced mine yesterday, my hubby and I threw in a bunch of grass and stayed inside the enclosed run to keep the pecking to a minimum. There will still be the pecking order that has to be established, but un-necessary roughness is not needed. A few reminders from you the "alpha roo/hen" will remind them you rule that roost.
