I remember, on at least one occasion as a kid, seeing parts of a movie on TV which totally freaked me out. I mainly remember seeing a boy walking around on the roof of a house while talking backwards; kind of like the weird Twin Peaks effect where they rewind the voices. There were police or other adults that thought the boy was important and wanted to catch him, but he was wandering into hard to get places.
I think I saw it on TV a second time, which freaked me out again, and that's when I learned he was the witness to some murder. Possibly of his parents. It may have even shown flashbacks to the murder (which I believe was in their bedroom). I think they were trying to get clues out of the boy and that's why they were chasing him around. Although it's probably good to get any child off the roof as a general rule.
I have no idea why he was talking backwards or why he was on the roof, but it was very unsettling to me. I thought for sure this would be an easy one to google with all the details I remembered, but none of the movies that came up sounded like the right one, or even mention a backwards talking boy.
Grayson K
IMDB The Window 1949 To avoid the heat of a sweltering summer night a 9-year-old Manhattan boy decides to sleep on the fire escape and witnesses a murder, but no one will believe him. (Tommy/boy witnesses his neighbors murder someone but his parents don't believe him due to his constant fibbing.)
I saw a movie called The Window 1949 and it sounds a little bit like your movie. I haven't seen it in decades and I don't recall any backwards speaking boy but I did find mention of a boy possibly 'mumbling'? in his sleep on a roof.
https://tvtropes.org/pmwiki/pmwiki.php/Film/TheWindow
Make It Look Like an Accident: Mr. Kellerson tries to make Tommy fall from the fire escape to his death but Tommy only faked his drowsiness and escapes onto the rooftop.
Archive is temporarily down so I couldn't search for the rooftop scene.
https://archive.org/details/TheWindow1949BarbaraHaleENG
Update: I Found it!
Me and my gf searched for awhile more and finally found it. It was a movie called Silent Fall. I think the part that threw me off was that the boy apparently didnt talk backwards.. he mimicked peoples voices by playing them back with his mouth like a tape recorder! It's pretty cheesy and not nearly as creepy as I remembered it being.
Apparently you can watch it on this Tubi streaming website (you dont need to sign up either). The scene of the murder and subsequent run to the roof of the house begin at 0:51:00
https://tubitv.com/movies/502444/silent_fall
-Grayson