When I was young, I envisioned a period to be a red dot about a centimeter in diameter. I can't remember how, but I knew it was 'down there' somewhere. So when I heard of a girl having her period, I would visualize this red dot appearing there. I thought that once they got it, they just happened to have a red dot there, for no particular reason, but that it was a part of growing up.
A childhood belief about periods

others believed things like this
- In 6th grade, I thought that once you got your period, you'd have it forever!!!! 24/7Anon
- I thought that your period came out all at once and you had to wear a pad around the time it would come.— Sarah
- i used to thought that period is when you pee like a baby for a few days...— i'm totally weird
- When my brother would go by condoms i thought that guys had period and that is what they usedAnon
- When I was a kid, I found out about a womans period and I thought that she would bleed through her breasts.— Michael
- I used to believe period blood came from the nipples. I thought that was what "padded bras" were for!!Anon