If you put dishes with chick crumb on the ground and the feeders with layers pellets much higher up out of the chicks' reach they can mix from a young age if the other adult hens aren't nasty towards them. It's ok for adults to eat some chick crumb.
I have a run within a run system (broody coop with run inside much larger general run). As long as the chicks and mum were still going to bed in their broody coop at night, then after they went to bed I put chick feed in their own little run and shut their run door. After they had eaten quite a bit the following day I'd open their little run again and they mingled with the rest of the flock.
Remember to make the heras panels not just fox but also chick proof, it's amazing how small a gap a chick can get through with a bit of sheer dumb luck
I use mesh with 1inch gaps. When chicks get out they can't necessarily find their way back in.