I once thought that the electrical wires that came with Erector sets contained electricity, and if you touched the metal ends (as opposed to the insulation) by accident, you'd get a shock.
A childhood belief about toys

others believed things like this
- I used to believe that Metal music was when a bunch of people would bang metal together to make noise. Ha ha.— Kassandra
- As a kid, I thought "No Outlet" signs meant the houses past that point didn't have any electrical outlets.— Julie
- I used to think that when you sent a fax, the paper went through the wires.— em
- I used to think that a conductor while conducting told the players what to play as opposed to their music.— Daryl
- When I was a child, I thought that the Heavy Metal was Satanic music.Anon
- I used to believe that bird perched on telephone wires to keep their feet warmAnon