When and how do I introduce baby chicks to the coop? My hen was sitting on eggs, they started hatching 3 weeks ago. So the babies are now about 3 weeks old. They are already getting their feathers in. I'm still using a heat lamp on them at night because they still shiver without it. Anyway how old do they have to be before I can let them into the coop, and how do I put them with the big ones??