Both my parents coincidentally have the same last names, so when I was little, I always thought that you can only marry people with the same last names. i.e. your brothers/sisters...
A childhood belief about names

others believed things like this
- As my parents had given me a name, I thought that it was up to me to give them names tooAnon
- I used to believe my parents names were mom and dad till i was 9— Sophiae
- When I was very young, I believed that my parents actual names were "mum" and "dad". — Margo
- I used to wander what my name would be in other languages. I thought that names worked the same way as words. — Simon
- For along time I thought the Middle East and Eastern Europe were just different names for the same place!— Helllowerer
- At the age of around five, I realized that my mum's and dad's names were not mum and dad!— yelloworpurple