I used to believe that the sex of the baby was determined by the length of the pregnancy at birth.
My mother once said, when I was about 5, that if I was born eirlier, I would have been a girl. Much later I found that she said that because she had a miscarriage of a female fetus before me. :(
A childhood belief about giving birth

others believed things like this
- Until I was five, I used to think that women gave birth to baby girls and men gave birth to baby boys— Cassidy K
- I used to believe that a baby's sex was determined by whether the sperm had a picture of a man or woman on it.— David E.
- I used to believe that when being born, your mom would give birth to an egg, and later you would hatch— Becca
- I used to think that if you didn't have a birth mark you hadn't been born.— Kim
- I used to believe that birth control was for deciding to have either a boy or girl babies. Anon
- I used to think that to give birth, a woman had a slit cut into her inner thigh, and the baby would come out.Anon