The older chooks might hackle your chicks if they still have down. I know my Silver Leghorn chooks hackled my Barred Rock chicks when I first got them. Hackling is when the bigger bird tries to get the smaller one into submission. No one is hurt, but it does look aggressive. They'll continue to hackle even when they're all grown up! It's like campaigning, the bird gets as high a rank as it can in what is called the Pecking Order so that it gets first dibs when a hen to the nests, feed, and sleeping areas. That's why roosters fight, sometimes even hens will fight, to get the other into his place in the Pecking Order.