Our head rooster is a bit hostile towards the younger chickens as well. He's just trying to assert his dominance as alpha to the new arrivals, but we have had to take measures so that the newbies have someplace safe to go where they can eat and socialize without him trying to push them around. Once they fully mature, he is happy to accept them into his flock, hen and rooster alike, so it'a transition we tolerate.
The biggest problem with integrating youngsters is that the adults may not intend them any harm, but they can kill a chick out of innocent curiosity. I love that we got broody hens this fall, because they helped the integration progress much faster than it otherwise could have. Whenever a curious or wayward adult wandered too close to the babies, the mama hen put them quickly in their place, and they soon learned to respect not only her, but the chicks in her care. For this reason alone, we are able to have our 6-week-old chicks mixed with the rest of the flock of adults unsupervised.
The thing that blows my mind is that one of our bantam cochin roosters has been mingling with the broodies and chicks, and seems to be as interested in caring for the babies as the hens are. It's quite a sight!