I have 4 pullets that I think are around 3 months old. Their coop has an "upstairs" with a roost and nest box but they don't seem to have an interest in sleeping there at night. Instead they pile on top of each other in the front-most corner of the coop. There was a raccoon attack at the nest box a couple weeks ago on a night they had decided to sleep in the roost area (but still just in a pile and not on the perches). Could this have put them off sleeping there or is it just that chickens don't really roost until they're grown? This is a pic of the coop to give you an idea of what I'm talking about:
