The chicks need a separate 'coop' and run for right now. It doesn't have to be fancy. A dog crate for sleeping/shelter and some wire fencing and metal posts for a run will do. The idea is that each group has their own space, so as to not feel threatened, but they are close enough to get used to each other. After a week of this, you can open up the chicks' temporary run into the adult run. Gradually, the chicks will start to spend more time in the adult area, and less time in their area. After a week or two, they will move themselves into the adult coop.
The key to integrating any group of chickens is ample room for all, and multiple food and water stations. Chickens can be very territorial, and that's why gradual introductions are so important.
It takes longer than a week, and the chick setup can not take up the adults' sq footage. That's a big one. You want the introduction setup right next to the adult setup, not inside the adult setup, reducing the amount of space the adults have. The chicks get their own space, the adult's have theirs. Then, after at least a week, you can let the chicks mingle in the adult run, but make sure that they still have access to their pen, and that the openings are too small for the adults to get in through. And have at least 2 or 3 food and water stations.
I have (3) 5 week old Easter eggers that I am trying to introduce to my 3 year old hens. I have had them in a secure spot in the run during the day for about a week so the other girls can get used to them. We tried introducing them and our buff Orpington flew over and viciously starting attacking - I had to pull her out. Now she paces around the area and looks for any chance to get near them. I've had to lock the older hens in our covered run at night (they have roosts) so the 5 week olds can sleep in the coop. Then I have to put them in the secure part of the run during the day so the older girls can lay. I know some pecking order needs to be established but she would kill them if she had access. Any suggestions? Should I wait until they are older and try again hoping the buff will calm down? I've never had any aggression in my hens with each other.
The little ones might be too young to introduce to the hens yet. Ten weeks would probably be better. I've pushed it to eight weeks but that is always after a month of having side by side runs.