I always let my hens decide for themselves when they want to leave their chicks to it. Depending on what you are then going to do with them I'd do one of few things
a) Just let them all go into the main hen house with the others. Mum will probably go perch if she is ready to leave them, if not she'll sit on them still. The chicks will probably then all go cuddle up in a nestbox or on a perch together.
b) Wait for her to stop showing willing to sit on them.
c) Remove her from them and put her back in with the other hens. Then keep the chicks separate in the current set up till you wish them to mix.
I generally find the older hens more accepting of youngsters if they go in with their mum before she stops sitting on them. And easier to then look after as I don't have to deal with chicks in one place and hens in another. I also usually let a hen with chicks mix with other hens and my cock birds from when chicks are about a week old. The cock bird is usally very good with them and finds food and watches over them. Also the hen will tend to keep to herself with the chicks and tell off any hens trying to intefere. I only ever step in if their are obvious problems with the hen and chicks and the others. I actually find this approach of allowing them to mingle in the daytime far more harmonious than keeping them all apart.
