S.
Have you tried sitting in the boy's room after dark. Since both children are scared of the room, there may be a specific reason for it (i.e. noises coming out of air ducts, scary shadows from trees, etc). Do a little detective work. On the other hand, I have a 4 year old. She plays in the bed till she goes to sleep. My 7 year old did the same at that age. It's possible that he remembers his sister being afraid of the room and is mimicing her.