You need to keep them separated for a few weeks, in the coop would do, but put the younger ones in a separate cage...so they can see each other but not get to each other.
I did this: I had the cage in the coop, let the older girls out to free range, shut off the coop and run, then let the younger ones out. I did this for a few weeks, at night I caught the little ones, tucked them back into their cage, then let the big girls in.
Eventually, a couple weeks, you will have to let them mingle...it is advised they are close to the same size...give the little ones a safe place to run to...in my case it was the cage...they will get pecked, it will break your heart...but its the only way...pecking order must be established.
Just stand by and watch...make sure they have a place to run to!
They will get adjusted and learn their place. I have almost 2 flocks now...my main one and the 3 EE pullets...they eat together finally though, but don't free range together.
this was my set up.
Good luck!