I don't have any pics, but when my birds where at that age, I fenced off a 6x16 area inside my pen with 4' chicken wire to keep them in. Then they learned that they could fly, and they flew over into the big pen and didn't understand how to fly back over, so I made openings in their pen that they could fit through but the larger birds couldn't.
This worked until they stayed in the larger pen more than the smaller pen, so I just removed their temporary pen and all is well.
Now I'm back in the same boat again, I have some White Leggers that are about 12 weeks old and I have them in a temp. pen inside of the coop, but I will have to move them soon.
Keep in mind that when you introduce new birds to your flock, they are going to go through their pecking order again.