It seems almost all the posts people have on this movie are memories of watching it as a child, and then having vague memories of bits and pieces as an adult...
I must say, I'm not much different in this matter either. All I could remember was bits and pieces of the plot line. I do remember getting nightmares from it (like most people), not that this is particularly a scary movie by today's standards, but to a child it definitely puts a psychological fear that stays with you. So I looked it up, trying every search word I could think of, (i.e. hair loss, regrowth, solution, paintbrushes) Ehh... after browsing through tons of rogain ads, I finally came across it. I managed to find a copy and watched it again.
It's actually a truly unique movie. A novel idea about a kid who loses his hair, and gets more than he wishes when he applies a magical hair-growth solution. I think perhaps it wasn't marketed correctly back in the 80's because while it seems like a childs movie, I wouldn't recommend it to young children. Maybe not just the marketing either, but the movie itself would've probably been able to stand on its own without being characterized as a child's movie. I would bet that there are probably even people today who have been scarred from watching this as a very young child...
So, if you come across it, it's worth checking out. But sensor before letting your kids see this one!