I used to think World War I and II were actually pronounced War War I and II.
Took me about 11-12 years to get it straight.
A childhood belief about wars

others believed things like this
- When I was little i thought lb for pounds was pronounced lubs, and i called them that for 2 years. Anon
- I used to think making straight A's in school was literally writing A's straight. Anon
- Until a few years ago, I believed this was a "doggy dog" world, rather than a "dog-eat-dog" world.— jemima
- When I was 6 or 7 years old, I absolutely believed that if a thermometer broke--the world would end. — Suzi
- i used to believe that 'island' was pronounced 'is-land' instead. I know im not alone on that one! :)
— Da KornMeal - I used to think that New York was pronounced "Yew Nork"Anon