Hens go broody when you don’t want them to… and won’t go broody when you do. 
Watch older birds with ones that young, i am letting my 4wk olds roam a bit with the flock but "technically" they have their mama but she's a bit over the concept lol I also have two drakes, so i watch, i don't leave them without my being there BUT these birds have all see babies before so i kinda know how they react in general.
My 4wk olds have been raised in the duck barn, now yes they have mama but at this aging she hasn't covered them in at least 2wks... so i have a lamp, i actually downed it to a 175 about a week ago, we have been below freezing up till lately, they are doing fine.
The key is knowing what temp your inside is, i always have thermometers in my buildings so i know where we stand...
My 4wk olds have been raised in the duck barn, now yes they have mama but at this aging she hasn't covered them in at least 2wks... so i have a lamp, i actually downed it to a 175 about a week ago, we have been below freezing up till lately, they are doing fine.
The key is knowing what temp your inside is, i always have thermometers in my buildings so i know where we stand...
