How high is the nest? Chances are the chicks will get down fine, unless we are talking about a second story hayloft, and even then they might. They might have trouble getting back up at first, though.
If it's only up a foot or two, make a simple ramp or steps with concrete blocks, anything handy, when they hatch. You'd be surprised how far they can jump.
Not everyone here separates a broody or new mama from the flock; I don't separate the mama. I did separate her as a broody, still in the coop but in a wire cage, just to keep the others from pestering her. When the eggs hatched, I removed the cage. And I let her out every morning, plus kept food and water in the cage. A good mama will protect her chicks from the others, as needed. If you don't separate her while she sets, do mark the eggs (pencil, Sharpie) and keep a check, because they will steal and switch the eggs around.
