When I was little, I went to a clinic and accidentally misread the information on the poster there. So, after that I came to think that women get "big boobs" (as compared to having no chest at all) only after they give birth to a baby and breastfeed him or her. For some time I went around looking at womens' chests and "knowing" whether they already had children or not.
A childhood belief about rude bits

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 think that to give birth, a woman had a slit cut into her inner thigh, and the baby would come out.Anon
- My niece believed that the longer I breastfed my baby the smaller my boobs would get. She was 4 at the time.— M
- I used to think that if a women had a large chest she had babies inside them.— Emily
- I used to believe that women gave birth to girls and Men gave birth to boys— Rob
- i used to think that women gave birth to their husbands and marry them...— Pat