Merging Chickens

[southlake chick]

I am new to the whole chicken thing. It all started with my 14 year old daughters science fair, next thing you know I have three beautiful chickens and have built a coop, they are 6 months old and one of them(?) is now laying. So.... I hatched 9 more, they are one month old bought 8 more that are 3 weeks old. So the question is how do I merge them all together? I have stables that are divided and when I came home the three older ones were in with the 9 that are one month old. They were getting along fine, when i moved the 9 into the coop where the 3 older ones live the big ones pecked at the little ones, any suggestions?

 

[DaughterOfEve]

all chicks or all full grown birds merge together better. By about 3 months old the younger ones should be big enough to deal with the older birds.