I was real young when I watched it, so I do not remember much. I remember that there was this old house, I think that it was abandoned and there was a group of kids (maybe teens) that went to this house and someone went down into the floor of the fireplace. I think that they might have found the body of a dead girl down there. That is all I remember except that it was really foggy around the house. My sister and I watched it when we were really little and it scared the bejeezus out of us. We are both trying to find this movie but that is all either one of us can remember. If you know anything, please help me. Thank you!

Kind of sounds like the haunting, but they were adults

Sounds like Don't Be Afraid of the Dark, 1973, except for the kids. If so, thank Quinn F from this post. (https://www.askmehelpdesk.com/movies/names-2-horror-movies-late-70s-80s-249794.html?highlight=70%27s+horror)

It could be Mystery Mansion.