Let them out once a day for a few weeks as they grow older. Put some food in a place nearby wherever you want them to sort of stay around once they are free ranging, and let them have access to that food during the times you let them out. Once they have figured out that that is where their food will appear everyday, they will have no problem staying "around" that area. They probably will not stray far from it, even when they are free-ranging. My chickens always stay where they can see their food. We live on 25 acres and they don't go but maybe 50 yards away from their food at the farthest. The ones who sleep out of the coop at night even have their sleeping spots within 20 feet of the food.
Good luck!
p.s. Don't forget that when you free range their is a much bigger chance that something could happen to them, regarding predators.