My mum once attempted to explain the circulatory system to me, including the bit about valves that only open one way when the pressure of the blood behind them hits a certain level (or something). I got the impression that this happened because you were moving about and that if you ever stopped moving the valves wouldn't work, the blood would pool in one limb in your body and eventually that bit would die. I blame my inability to sit still on that bit of badly explained science.
A childhood belief about general

others believed things like this
- When I was about 4 and I saw the clouds moving sideways, I thought that Earth was moving closer to the Sun— Helen
- when I was young, I heard that blood had iron in it. I thought blood was red because it was rusty.— Hunter
- I used to believe that when I saw the clouds moving in the sky, that it was actually the earth moving. — Megan Gilbert
- I used to think that instead of bones and blood and tissue that you body was made up of tuna.— m.n
- I used to believe that guns shot out blood because everytime somebody shot a gun in a movie you saw blood.Anon
- when i was litte
I used to believe that white people had white blood and black people had black blood.Anon