You don't have a typo in the age, do you?
Chicks that are 5 to 6 weeks old would be almost fully feathered. They do not need a broody hen to be their mother, and they mostly do not need a brooder either. They just need what any adult chicken needs: safety from predators, protection from bad weather, not being bullied by other chickens. When chicks are raised by a broody hen, it is common for her to quit mothering them by the time they reach 5 or 6 weeks old.
But if the chicks are 5 to 6 days old, they still have a lot of down and not many feathers. They do need a source of heat (hen or heat lamp or brooder plate or something) and a bit more care than when they are older. Introducing them to a broody hen might still be difficult, because the chicks might not accept her as "mama" when they are that old. A hen is more likely to accept chicks if she has been broody for about three weeks, instead of just a few days.
All hens are individuals, so things like how long she must sit before accepting eggs will be different from one hen to another. Likewise, some hens will not accept any chicks, or will not accept chicks that did not hatch under her, or will not accept chicks of a certain color, or will not accept chicks over a certain age. Other hens do seem willing to accept any chicks, any age, any color, etc.
