I used to think that people could guess your birthday month if your parents were known for trying to conceive at a certain time of year, that being 9 months
Beforehand.
A childhood belief about sex

others believed things like this
- My parents have the same birthday -- month, day, and year. I though all mom's and dad's had the same birthday.— Cait
- My birthday was on a different day every year, assigned by my parentsAnon
- I used to think that your birthday changed every year, and that your parents just decided what day it was.— Daniel
- I used to believe that on your birthday everybody would worship you! (I guess I was wrong).— supergirl
- iwas told that if u cry on your birthday you would not get any bigger 4 a whole year— steve
- i used to think that if i didn't celebrate my birthday each year my younger sister would catch up with me— q