When I was fairly young (quite possibly four or five), I was fortunate enough to have a fairly good scientific grasp on how reproduction occurred - at least, as far as the sperm and the egg went. Exactly when and how this happened, I wasn't quite sure - but my personal theory was that while the soon-to-be parents were sleeping in the same bed, they somehow gravitated toward each other, and while sleeping, did something that caused conception. Exactly what this 'something' was, I really didn't know.
A childhood belief about getting pregnant

others believed things like this
- When I was a child, I used to believe my parents were superheroes, like the fairly oddparents!Anon
- I thought until fairly recently that bacon came from the skin of a pig and that's why it was so thin— Nate
- My parents said that gnomes tied knots in my hair while I was sleeping. I had insomnia for years.— Daria
- I used to believe that aliens would come and take me if I wasn't good to my parents— somebody
- i used to think that when a fish floated to the top it was sleeping.— Kriket Evens
- I belived that santa came every night to se if i was sleeping— david