The way we did it was we let them play together in the big run, with me in it too, when they were around 3-4 weeks (it was warm outside). Then I moved their cage into the run. Then I moved them into our bottom coop. The door can be open halfway. The chicks can go in and out into the run but the hens cannot go in. They venture out, if a hen comes at them they run into their coop. I have food and water inside theirs so that if they do not want to come out, they dont have to. They do quite often. This has been about a week (they are 5-6 weeks now) and the hens are starting to tolerate them, except during treat time. I have to give a bunch of treats to the hens and then run over to the opening of their coop and drop some treats there. (They grab them and run it.
Though I gave them some pieces of a plum and a couple of the chicks ran and took them out of the barred rocks' beaks and then ran into their coop! I thought that was pretty brave, I guess that is how much they love plums! It was funny too cause the chicks run faster than the hens and those girls sure tried to catch them lol.