I have a two week old chicken that is kept separate with its mother from the rest of the flock. The couple of times that I have let them out with the other hens the larger ones - Blue Astralorp and the Wynadotte are very aggressive to the chick and peck it quite hard. These two hens are the "bullies" of the flock and peck the other hens. The mother is very protective towards the chick. When is the best age for the chick to become part of the flock on a more permanent bases. The mother and chick sleep in their own little run on the ground and the others use the coop above. This is my first time raising a chick and it has been a learning experience. Thanks.