I used to believe that a man only had six sperms (I somehow got confused when my mom was telling me the facts of life) and I couldn't quite figure out how come my aunt and uncle had seven kids.
A childhood belief about reproduction

others believed things like this
- I used to think Uncle Ben and Aunt Jemima were a married couple. — l stu electtirc boogaloo
- I used to think that your cousins are your cousins only until they're 21, then they become your aunt,or uncle!— AMILA
- I used to believe that "euthenasia" was "youth in Asia", and I couldn't figure why that was A Bad Thing.— Kellye
- I thought cartoons were for kids and "real-life programs" for adults.— Ichigo
- I used to think grown ups couldn't lie...especially not to kids.— Jessica
- when i was really young, i couldn't figure out why i can't get older than my older sister.— angela