We have a large coop with a chicken wire pen inside it, about 5' x 5', which has been used for several things, including a setting broody. When the chicks are up and running around at about 2 days, this area is opened up, and the mama raises the chicks mixed in with the whole flock. Everyone is fed something besides layer so the chicks won't get too much calcium (flock raiser, grower, even starter) and oyster shell is offered separately for the laying hens. The chicks don't seem to bother the oyster shell.
With each batch, both the mama and the chicks obviously wanted out of their pen to be with the rest of the flock.