OKAY so I've had a hen hatch out babies twice this year and I'll answer what I can, with my (limited) knowledge.
Generally around 5wks old, the hens do start distancing themselves from their chicks. 5 weeks is a good age for chicks to fend for themselves, especially if you let them free range. I had her raise 3x chicks and then another 3x to start (as these were her first two broods), and around 5wks, once she starts laying again, she distances herself by chasing them off or simply leaving them behind.No amount of the scared, shrill baby cheeping got her attention once she unattached herself.
My second batch of babies got left behind right as soon as my hen started laying eggs, and she wouldn't have ANYTHING to do with them once they were away from her, and those three babies were huge and could free range with the best of them at 5wks of age... plus they were master escape artists and knew our yard like the back of their wings.
If baby chicks are outside, their feathers come in faster and they'll stay warmer, but they will need an area to go to that's their own, so they can bundle up and stay warm. Start getting them roost trained ASAP, so they stop sleeping and pooping in nests. The older they get, the harder it is to break that cycle of them wanting to sleep in nests. If they're already separated from the flock in a hen/chick enclosure, keep them in there until they're large enough to stand their own against the other hens - the other hens can and will kill small chicks.
If you're unable to keep the chicks away from the large hens due to not having a brooding area, you might have to bring them in! But I'd invest in a brooding coop (it doesn't have to be big - a rabbit hutch sized one would do fine for a hen and a couple babies) this coming spring, if at all possible!
I hope this helps you out somehow!