I am wondering how to do this, too. I have a VERY small flock (two barred rocks) and am planning on addding 3 new chicks this year. The barred rocks will be about 1 when we will be getting the new ones. Thanks for any help or advice!
Well, it is easy enough. The chicks will outnumber the adults, but the adults will be the superior. The chicks should be introduced when they can at least (somewhat) hold their own. I wouldn't do any sooner than 6 weeks. They will get picked on, it's inevitable, the adults will try to establish the pecking order. They will be 2 seperate flocks for a while.
The chicks could have, well, a hideout though if you want. At least that's what I call it. Others call it a panic room. In the coop, when I first introduce chicks, I have a box that contains ome food and water for the chicks. The entance is only big enough for them, not the adults. I locked them inside it for 12 hours, then let them out, so they know where it is. So whenever they are getting chased or picked on, they can run to their hideout, or panic room. And as the chickens get bigger and they all get used to each other, you will have no more need for the panic room. I take it out usually within 2 weeks. At least for me, it doesn't take that long to integrate new members to the flock. Yah, they will be lower on the toten pole for a bit, but as long as your older chickens aren't trying to kill them, there is no problem. And it will only get better as the chicks get older and become more a part of the flocks. For me personally, within 5-6 weeks of me putting the chicks with the rest of the group, they are all one big happy family!
I'm sorry if I'm making this sound complicated. This is actually just one way to do it. Quite frankly, there have been several times that I've just take a group of chicks, throw them into the coop and say good luck. And you know what? It works fine. Sure, they get picked on for a few days, but I have NEVER had a chick killed by an older member of my flock. Other people will say otherwise of course, but this is just my personal experience. So whatever you want to do with your chicks, I say do it! Either way, I have actually never found it that hard once I just commit and make a decision on what to do with that particular group of chicks.
Barred rocks really aren't that aggressive. I've had them before and they are very sweet birds! I don't think you will have any serious problems, mostly because there are just two of them!