I used to think when babies were born that the parents would decide whether to make it a girl or a boy by chopping the umbilical cord to size. That is, if they wanted a girl they would cut the umbilical cord short (leaving only the clitoris -- which I thought was a tiny penis), and if they wanted a boy they would leave the umbilical cord as long as they wanted to make the penis.
A childhood belief about rude bits

others believed things like this
- I used to believe that babies were attached to the umbilicle cord and then stuffed down the throat grow.— anonomous
- When i was younger i thougth that when you grew up you could decide whether you wanted to be a girl or a boy. Anon
- when i was a little girl i asked santa for a penis for christmas. i thought it was a really awesome toy. — haha
- I remember a girl in my kindergarten class told me she wanted to be a waterfall when she grew up.Anon
- im a girl and i used to think my mom had a penis and i would eventually grow my ownAnon
- I used to think that oral sex was when the guy put his penis in the girl's belly buttonAnon