You'll want to introduce them slowly. If you can, put a temporary fence around part of your run for the 2 month-olds. Move the big hens' feeder and the 2 month-olds' feeder to that temporary fence so that they are eating next to each other every day but can't pick at each other. After about a week, if possible, make an opening in the temporary fence big enough for the littles to get through, but small enough that the big hens can't get through without really trying. Eventually start only feeding on the big hens side. Once everyone seems to be acclimated to each other, remove the fence. It takes a different amount of time for every flock to get used to each other, so you'll really just have to watch and decide based on how your hens are acting. If they start picking on each other, just go back a step until you're ready to try again.
