When I was a child, my mother referred to vaginas and penises as "pee-ers". You use it to pee, therefore, it is a pee-er! I truly believed that this was the technical term for them. It took years for me to understand that she only called them that since peeing is what they are used for.
Imagine my dismay when I when I started school and heard my teachers talking about being nice when playing with your your peers.
A childhood belief about rude bits

others believed things like this
- When I was younger I thought men had two penises, one for peeing and one for having sex.Anon
- I believed that our teachers lived at school. They were teachers--they had no reason to leave :)(Anon
- when i first started school i thought the teachers lived in the school and slept on the tables.— emma
- i used to think that the term 'necking' referred to boyfriends and girlfriends who rubbed their necks togetherAnon
- When I was a child, I used to believe that teachers never leave school and slept in the chairs.— Majo
- I used to think that teachers were all nice. — name