When I was about 9, I had just started learning about sex. One day my neighbor asked "What sex are you?" I replied "Safe." He obviously meant Male or Female.
A childhood belief about sex

others believed things like this
- I used to think that to desex an animal meant to turn it from a male to a female or female to male.— Phil
- I used to think that when you had sex the male was sucking the life out of the female!— dude
- I used to believe all cats were female and all dogs were male.— Sabby
- I used to think that all cats were female and all dogs were male. — Annalisa
- i used to believe that all cats were female and dogs were male!Anon
- I used to believe that cats were all female and dogs were all male.— Rachel