We frequently give our broody hens chicks to raise, easier for us and so much nicer for the chicks. We don’t separate them from the flock at all, but just sneak the chicks under the mother hen at night and when we are confident she has accepted them, move her nesting box and chicks into the henyard next to a dog crate which contains the chick starter and their water. She will protect them from the other hens and the dog crate allows the chicks to access their vittles while keeping the big girls away. You can see it all here:

Another advantage of this is that I don’t ever have to worry about reintegrating mama and babies back into the flock.