When I was a kid I remember watching a TV movie. It was an old house and a group of kids were playing around. It was something like a backyard and this big old house. Some of the kids went inside to find out there was a girl dead for years or decades and maybe a skull or something was there to see on a fireplace or chimney. Any clues? Thanks.
Mystery Mansion (1983)...?
Susan (Randi Brown) and her brother Johnny (David Wagner) come across an old map that may be a clue in finding gold, while staying at their aunt and uncle's house. Susan has been having nightmares about Rachel, a young girl who vanished in 1889 from a nearby mansion when her parents were killed by bank robbers. The siblings make friends with Billy and soon began their search for the treasure as well as find out what happened to Rachel.
From an IMDB user review:
One scene that I remember (spoiler) when the 2 children find the secret entrance to where the treasure was hidden. What they found is what always stayed with me. They found a pit that at the bottom of contained the bones of the missing girl Rebecca.