Weaning them means the mother has left them on their own to make their way in the flock. She no longer protects them, finds them food, or keeps them warm. The chicks are no longer her total focus but she goes back to the rest of the flock to eat and roost. She will build up her reserves and start laying eggs again.
Normally a hen does this all at one time, but I’ve seen hens continue to take care of her chicks at night while leaving them on their own during the day. I’ve seen hens take care of the chicks during the day but leave them on their own at night. The standard method is all at once but like everything else in the chicken world, there can be differences.
I have seen hens wean their chicks at 3 weeks, though that is really young. Four to nine weeks seems to be standard, but some will continue well after that. The hen will have integrated the chickens into the flock before she weans them but the chicks still have to manage the pecking order on their own. Since they are immature the older chickens (practically always the hens, not the rooster) may beat up on them if they intrude on the hens’ private space, so the younger ones tend to form a sub-flock within the flock and avoid the adults until the chicks mature.
