I completely thought sex "happenned" while you slept. Thus the phrase they slept together!
A childhood belief about sex

others believed things like this
- I used to believe that if I slept on my tummy my boobs would never grow so I never slept on my tummy.— LoLo
- I thought all the teachers slept at school.— Ryan
- When I was little, I thought that if I slept with socks on, my toes would grow together.— Laura
- When I was a kid, I slept with my fists balled up because I thought if I didn't, E.T. would eat my fingers. — Brian
- I used to only sleep on my back because I thought I would break my ribs if I slept on my stomach.— Molly
- I used to think sex was whenever a man and a woman slept in the same bed.— confused