4 weeks might be a little earlier than some hens ween, but many hens do ween that early. If these chicks have been in the run with the adult birds, the adult birds will not harm them. Leaving a broody hen and her chicks with the flock is the way many manage their flocks. A little peck here and there is normal from the other adult birds to give the chicks. The chicks need to be shown the coop is home. Guide them in to the coop. (catch after dark in necessary) Make sure they have places to hide from the adults. Locking them in for a day or two could help. It is up to you if you want to keep the older birds in or out while the young get use to the coop.