There is the common children's belief that stars really are tiny things shining in space, although they are suns, just like ours in the universe.
My cousin told me that "radioactive" meant "evil".
when i was i child i used to believe that everyday there was a new sun in the sky.
When I was a child, I used to believe that the force of gravity was an old woman named "Marialonga" sucking down children with her hands.
I used to believe that magnetism could "rub off" on you, like dirt or a smell. Like, if you touched a magnet with your bare hands, you'd get magnetism on you. And then, if you put your fingers in your mouth without washing them, you could swallow the magnetism and it would close up your intestines.
To this day, I still feel uncomfortable touching magnets!
As a kid, I once tried to named as many colors as I could, and I got 21. For some reason, I was convinced there are exactly 4 more colors. I even "discovered" them later, except I still didn't know what they looked like.
When I was small I had a toy measuring tape that marked every centimeter (about 0.4 inches). I came to the conclusion that a centimeter is the smallest unit of length. So when something was, let's say, 0.5 centimeters long, I though it's either a measurement error or a pure illusion.
My mum believed that cold water would come to a boil sooner than warm water so I believed it too until school set me straight.
One of my first days in preschool I stepped on a crack and one of my classmates freaked out saying that I just broke my mom's back. When my mom picked me up I apologized profusely but instead of setting me straight she replied, "I was wondering why my back hurt all day." I avoided cracks for years until one day I got mad at my mom and stomped on a crack repeatedly. When it didn't work I assumed that it only worked with some cracks and continued avoiding cracks for an embarrassingly long time.
When i was a between the ages 3 and 6 I used to think that the moon followed me everywhere i went.
I thought the speed of light was different for fluorescent light since the fluorescent light in our kitchen would take longer to turn on than the incandescent light in our dining room.
When I was in 3rd grade I watched some cartoon where they mentioned Einstein and how he was a genius and came up with E=mc˛.
It gave me an idea.
One day when school was about to end, I took a blank piece of paper and in BIG letters wrote on it " E=mc˛ ". I signed my name underneath, left the sheet in the middle of my desk, and when the bell rung I went home. My hope was that my teacher would find it, would think I was a genius just like Einstein, and would advance me forward a couple grades! Needless to say my plan didn't quite work out :P
I thought that cold was an actual, positive force and not just the absence of heat
I thought that the universe was in the shape of a pyramid and our solar system was somewhere on the south side of it (yes I know there's no south in space but I didn't as a kid!)
My grandfather told me that when he was little, he thought that if you stood on an electric cord, it would block the flow of electricity.
Since diamonds are the hardest mineral, I thought that a train could be derailed by a diamond on the track......thought about putting an old diamond ring my mother had onto the track, but never followed up on it, not wanting to be the cause of a drailment in our town! - GOOD THING!
I used to believe that when it thundered it was God moving his furniture...if you have ever sat on a floor where people on the floor above you are dragging furniture it can sound quite similar to thunder.
I thought when the Big Bang happened it made an actual bang noise
I used to believe you could parachute with a bin bag. I realised my painful mistake upon landing but tried again anyway... a few times, just to make sure.
I thought that infrared was actually "info-red" because it gives you more info about the thing your looking at than normal vision (I wasn't sure what the red part meant tho)