I always keep chickens under cover in a temporary ranging area until they are too big for easy pickins' I just take tomato stakes, hardware clips, and deer fencing and make an area for them that is long enough to let them range but not so wide that it isn't easy to cover with bird netting. Garden staples in the ground to hold it down and prevent escapes. I sometimes put fisherman's net over the bird netting to decrease visibility and give them more shade. This temporary pen is put on grass inside the larger general area that the big birds are pastured in. This keeps them safe but still with the flock. If raised by a broody hen she is content to be in there with them because she has range space and she can teach them the ropes and keep track of them more easily. The makeshift deer fencing and stakes system is easy to move around because it's just clips and staples. However, it is secure enough if within a larger free ranging area where your adult flock is ranging or within a fenced yard. The larger area has another fence around it and as I described in the post above lots of areas for the adult chickens to take cover.
I never let babies loose without cover. You can cover them and still let them on pasture or grass. They do not need a huge area when they are so little. I know it's fun to see them running free but it's better to let them live longer and be free longer instead of just being free lunch.