The mom IS the brooder! She'll keep them warm and fed. I LOVE having mama hen's so much better than brooders.
Generally, the mom is do danged spit-evil to other chickens getting near her chicks, they don't bother. The last flock had only one casualty, but that was my fault. I left the water bucket full of water and the chick waterer went dry, so one chick drowned in the bucket trying to drink like mama did. But she protected them all from hawks, roosters, and everything else. Though, granted, there are some awful mama hens. You'll know!