There's a few threads in this vein at the moment, but I though I'd start one dedicated to Charley Says... and its ilk.
Most public information films creeped me out as a child (I think it was the sense of something bad about to happen), to the point where I used to try and avoid times where they were often shown. However, one that haunted me for years was the 'Grain Drain' one (warning farmers of the dangers of children playing in grain silos), which shows a doll sinking into grain with the sound of a child crying over it. I saw just a snatch of it when I was 5 or so, and the image stalked my mind for 20-odd years...