When I was little, I had an aunt who lived on Long Island. All I knew about Long Island is that it was "far away" (according to my parents!) from Boston and that being an island it must be across the water somewhere.
With this information in hand, I looked at the map in my Charlie Brown Encyclopedia and determined that Long Island was located in the U.S.S.R. When my friends came over I would whip out the trusty Peanuts atlas and regal them with tales of Aunt Nina in "Long Island, United States S.R."
When I was 9 we went to New York to visit her and I finally realized that Long Island and the U.S.S.R. were not one and the same. But only because we took a bus to get there and didn't go over the ocean.
A childhood belief about places

others believed things like this
- I used to think that Alaska was an island!— Draqula
- i used to believe that 'island' was pronounced 'is-land' instead. I know im not alone on that one! :)
— Da KornMeal - i used to believe alaska was an island because of the way they put it on our booksAnon
- I used to believe that Ireland was called that because it really is an island!Anon
- That the District of Columbia was an island in the Carribean. I believed this until I was about 19 yrs old. Anon
- i used to think easter island was called that because a giant bunny ran around and layed eggs there. — Oliver