I have 4 hens about 16 weeks old and 2 younger chicks (1 hen and 1 rooster) about 12 weeks old. We have had a lot of trouble getting young chicks to go in the pen with the older ones. The bigs ones really go after the young ones. Today we put the little ones in a wire dog crate in the big pen with the others. My husband built a door that is big enough for the little ones but not enough for the big ones. We put leg markers on the older hens (because I can't tell them apart) and it does look like one is the instigator of the problem. The babies are petrified and if they aren't in the dog crate they are really frantic to get out. I believe they have enough space. Now when they are free ranging they do seem to leave them alone (mostly). Ultimately I have to get rid of the rooster (inside city limits) but the hen is so attached to him and is so scared of the other chickens. The little hen is really the breed I wanted in the first place so I am feeling very protective of her. Any suggestions?