Thanks for the help/reassurances. The coop is alllllllmost done, but not yet. We'll try a wider roost in the brooder (which has always just been a holding pen with no supplemental heat) and keep setting them on there.
I've had four young chickens for the past two weeks. They're in a makeshift brooder in the house, and there are no older chickens. At this point, I have a 6-week-old, a 7-week-old, and two 10- through 12-week-olds.
At night, they don't go up on their roost bar to sleep. They'll sleep in a puppy...