From the age of about eight to ten I was convinced I could make 'Black light' by combining the beams from two torches - if only I could get them lined up right. Then I'd be rich. Oh yes. Well, I'm filthy rich now but still haven't cracked battery operated darkness.
When I was 3 or so, someone gave me a lava rock from the eruption of Mt. St. Helens (which 19 years later, I still have). I thought that if I put it in the microwave, it would become molten again.
I used to believe that records were the power source for record players.
Based on the "experiments" I used to rig up with things like old discarded blenders and other small appliances, I clearly believed as a child that electricity could not hurt me.
I certainly learned that it could blow fuses, though.
When I was small, I believed that if you ran the hoover over the power cord, or if you didn't keep the machine moving at all times, it would explode.
I insist that my mother told me these things; she denies it.
When I was 7 or 8, when the internet was still in its infancy, I went over to my cousins house to see his neat new computer, and check out the internet, something I had never seen before. He explained to me something called 'downloading', but didn't do a great job of it.
I was into stamps at the time (quit laughing at me), and I asked him if he could download any stamps for me. He said sure, and I spent the rest of the evening asking where they came out of the computer, while he tried to explain to me how they could possibly be 'in' the computer...I wanted them to come 'out'. I presumed the objects would simply come out of the floppy drive, but then I wondered what would happen if I wanted to download candy...some bars simply wouldn't fit in that small of a drive.
It was not until a few years later, when I started using the internet at my dad's work, that I figured out that when you downloaded things, they didn't come out of the computer.
Way back before I could read, I used to believe that typewriters were telepathic, and people just hit the keys as fast as they could and the typewriter would write out what you were thinking. So one day, my parents were letting me play with the typewriter, and I thought out a bunch of notes to people and pounded out gibberish with the keys. I then gave the notes to my parents and older children I knew, and thought they were just being mean and pretending that they couldn't read them.
i believed that you can send anything thru a fax and used to get puzzled why people only send paper and not other cool stuff.
I once believed that I could look into photographs, like you would a window, and look "around the edges" by holding them at an angle (also see further into the distance in the photo using binoculars).
When I was 3 or 4, I always saw my parent put video tape in the vcr. So I thought that my parent was feeding a monster. One day, my mother gave me a carrot stick. I decided I want to feed the monster. So I walked into my parent's room, jammed the carrot stick in (where you slide in the tape), and slided the carrot stick side to side. So yeah, I killed the vcr monster after that incident.