What kind of roosts do you have that they are falling off? I’ve had a broody hen take 2 week olds to my tree branch roosts and they did not fall off.
I’ve had broody hens wean their chicks as young as three weeks, I’ve had some wait until they are over nine weeks old. I’ve had some leave the chicks alone during the day but roost with them at night. I’ve had broodies take care of the chicks during the day but leave them on their own at night. There is no one set age or one set way broodies handle weaning. It’s remarkable how different the broodies can be.
Sometimes when Mama weans them the chicks continue to sleep on the roosts, usually crowded into a corner as far from the adults as they can get. Most sleep in a group on the floor in a corner instead of staying on the roosts. Sometimes they move to the nests to sleep, but I put a separate roost lower than the main roosts and horizontally separated so they had a safe place to roost. Having a safe place to roost higher than the nests keeps mine out of the nests. That separate roost is a 2x4, narrow side up.
After they are weaned my chicks normally form a separate flock during the day. They don’t intermingle that much with the adults, though some do more than others. The older hens outrank the chicks in the pecking order and often will peck them if the chicks invade their personal space. As long as the chicks don’t invade the personal space of the older hens there are usually no issues. I have extra feeding and watering stations and a fair amount of room so they can avoid the older birds. I think those help.