What you need are escapes, that the chicks can get to, that a larger bird can't follow. A lot depends on your coop/run. Post some pictures.
A pallet, in the middle of the run, up on blocks so just a couple inches off the ground, chicks can run under it from all 4 sides. I feed the chicks there. I have also used a larger box on it's side, as a outdoor shelter, with a wire fence in front of it, big enough for the chicks to get through it, and the big can't follow.
Personally, I get mine in there around 3-4 weeks. Being little, they are fast as lightening, and not that intimidating to the older hen.
Do add them on a day that you can spend most of the day watching to be sure.