None of our family gets on particularly well with my dad's parents, and my mum has always called them the "out laws" instead of the "in laws" as a joke. Until I was about 10 - well, until I learned what "in-law" actually means - I believed that your mother's parents were your In Laws and your father's parents were your Out Laws.
A childhood belief about family

others believed things like this
- Ironically my parents were born on the same day; so growing up, I thought all parents had the same birthdays. Anon
- My parents told me that when the ice cream van was playing music, it means he's run out of ice cream :(Anon
- I used to think that if you met your parents' boss, your parents would be fired!! AAAAAHHHHHHH!!!— Spoot
- I used to believe that all parents were called "Inge and Dirk", just like mine— eva
- On family road trips, my parents always told me that water towers were filled with chocolate.— Edith
- I thought that my parents chose my cousins, and was upset when my mother wouldn't let me add one.Anon