Was this a ghost?
When I was in high school, I used to baby sit for this family that lived in this big old house, set quite far back from the road. The house had three stories, and the third floor was a playroom for the girls.
One night I was babysitting, and I had put the girls to bed (they were 4 and 7 I think) and was downstairs watching television, doing homework. I went upstairs to check on them (because that's what a good babysitter does
The girls were both sound alseep in their beds, when I heard noises coming from the third floor (I figured I left a window open - -it was winter but you never know), and I noticed the light was on. (I would have sworn I turned it off when we left the play room)
I went upstairs, and the light was on, and all the toys were out on the floor. Window was closed and locked, there were no closets in the room, just an old couch and some chairs. NO idea what caused the noise, I put all the toys away (Which I swore I did before) turned out the light, and went back downstairs.
Bout an hour later, I checked on the girls again, and saw light coming from the third floor, I went back upstairs again (I was a brave teenager, who apparently didn't see enough horror movies) and the lights were on again, and all the toys were out again. Now, officially creeped out, I put all the toys away again, turned out the light, and sat on the second floor stairs, with a wiffle ball bat, for the rest of the night.
I mentioned it to the parents when they got home, they got very quiet, and said that it has happened before. NO explainations.... I never babysat for them again. They moved about 6 months later.