I have 3 chicks who are about 4 1/2 weeks old and up to now have been living in a brooder box with their mom. I am wondering at what age/size it would be safe to let them loose with the flock. I feel bad keeping them in that box but I would feel worse if I let them out only to get killed by one of the adult chickens in the coop. Any suggestions or advice would be appreciated. Thanks!