It was made probably in the late '40s. I want to say Ray Milland was in it, but I don’t think that’s right. It’s about a guy who just can’t get his life together, maybe even becomes alcoholic. (It’s not The Lost Weekend, I’m sure.)
Turns out, the whole time he was was suppressing a horrible memory from when he was a child: He accidentally killed a playmate by sliding down the banister in front of a brownstone and kicking the kid onto a spiked fence, impaling him. When the protagonist finally remembers, there’s a flashback where we see the playmate sitting at the edge of the banister with his back toward us and the star’s feet heading toward him.
Ring a bell?