Horror Movie with child and small haunted upstairs room

I have been trying to think of what this movie is to add to my Halloween scary movie list. All I can remember, is there is this mysterious small room at the top of the stairs in this house. The mom (and maybe dad) start to worry because their child is spending a lot of time in this small room (almost looks like a room you would find under the stairs). I can’t remember much else, but I think the parents can’t even open the door or the child goes in and can’t get out at some point. Possibly parent(s) finally get in the room and find weird things (maybe drawings?) indicating that the house is haunted and the spirit/demon lives in that small room. The spirit/demon mike take form of another child????