It's a horror movie, where a mother and her two children are in this house, staying with a mysterious older couple. A bunch of creepy junk happens, and at the end of the movie you find out spoiler for anyone who thinks they might want to watch a movie like this that the family was dead the whole time and they are actually ghosts.
Oh, and the kids were photosensitive or something, too. A lot of the horror came from the kids trying to get away from the sudden opening windows and doors. And there was one part where a piano was playing but nobody was in the room.
This was the only purely horror movie that I ever actually enjoyed, but for the life of me I can't remember its name.