Our chickens are about 26weeks old but we have just gotten some smaller ones. If it wasn't for the wire between the older chickens and the chicks I'm fairly sure they would peck the babies to death.

The chicks are oblivious to the danger they are in. The older chooks seem to think they are some kind of threat and are itching to get to them... That's why we aren't going to get them living together till the chicks are old enough to defend themselves.