My mom and dad happened to have the same birthday (dad is one year older). I used to think, similar to the way a wife changes her last name to her husband's once they get married, that she also changed her birthday to match the husband's!
A childhood belief about marriage

others believed things like this
- I used to think that your birthday changed every year, and that your parents just decided what day it was.— Daniel
- My parents have the same birthday -- month, day, and year. I though all mom's and dad's had the same birthday.— Cait
- When I was three I used to believe that cow and horse are wife and husband.— xenia
- When I was little I thought that a honeymoon was when the Husband and wife went to the moon and eat honey.— AmAnDa
- i thought I got one year older when my family sang the birthday song.— I am the ghost
- Up until I was almost 11, I thought that a birthday suit was a special outfit you wore only on your birthdayAnon