When I was little I used to believe that when you were born doctors would respect your privacy by not looking at your genitals and to determine your gender they would do some sort of blood test.
A childhood belief about sex

others believed things like this
- I used to believe that my choice of pyjamas to wear would determine the following day's weather.— Pyjaman
- As a youngster, my older brother told me that polish sausage was really the bull's genitals. — Ross
- when I was young, I heard that blood had iron in it. I thought blood was red because it was rusty.— Hunter
- I used to believe Nuns are a third gender, a cross between men and women:)Anon
- I used to think you could be gay or lesbian from kissing your own family members of the same gender.Anon
- I used to believe that guns shot out blood because everytime somebody shot a gun in a movie you saw blood.Anon