When I was 5-6 years old, upon reading about the invention of the steam engine and (in history textbooks) the invention of fire by cavemen, I thought the steam engine was invented in the same age as fire.

Anon

i used to believe that if you held hydrogen in one hand and oxygen in another and clapped that water would come out.
i just found out today and i'm 15.

H2O

The industrial part of my childhood town had a particular large stormwater runoff drain, at least large enough for one car to drive through, and for many years (I think i was 10 when i started questioning the reality of this gem) i honestly believed that if you stood in the drain you would be cloned. Yes cloned. This was 20 years ago so i guess i must have got the idea from Buck Rogers or some early sci fi crap

Daleen

When I was young, I figured out why yawns were "contagious." When someone yawned, they sucked in a lot of oxygen, leaving less for everyone else in the vicinity, so people nearby had to yawn too, to get more into their lungs. I still sorta believed it into my 20s.

SCB

This one isn't mine, but it's one my daughter picked up from me one day when we were driving. She was about 4 years old at the time and we were driving to the zoo for the day. We were passing a power plant with the two large steam silos that were giving off quite a bit of steam. My daughter asked me "Is that where clouds come from?", I was only half paying attention to here remark because I was driving but I responded, yes. We were driving the other day and she called me out on it. She's now 15 and knows better, but we both laughed as she confessed that she believed that's where the clouds came from until she was about 8.

Dan

I thought that deep space was 100% empty of matter, except for the random star, nebula, black hole, or planetary system. Since I always heard that space was a vacuum, I also believed that except for the dust and dirt inside a vacuum bag, I believed that the rest of the "space" in a vacuum bag was totally empty, just like space. I learned otherwise about the vacuum bag pretty early on, but I finally learned that outer space is not completely empty some time in 8th grade Earth Science.

Reid

You know how when your on the internet and you type the website in wrong, it usually takes you to a search website? well I used to think everytime the serch site came up, it was an actual search engine liek google so I always thought "Daing! There are WAY too many search engines!"

Deedee

When I was young, I used to think that if I picked up the phone while it was ringing then I would get electrocuted. I thought this because everyone that would answer the phone would wait until after the ring.

Rebecca

I used to believe that the toy chicks with the touch sensors were actual chicks trapped inside the plush and plastic shell.

Jeff-R

When I was young, my mother jokingly told me that cameras shoot out laser beams.
I believed that they would instantly desinigrate anything they hit so I was afraid of cameras until I was about 10.

Jeff-R