I used to believe that "wallaby" and "wobbly" were the same word (possibly pronounced "wabbly"), and that wabblies were called thus because of their wabbly ways.
A childhood belief about general

others believed things like this
- When I was young I used to think that WHSmith was all one word, and was thus pronounced "Wwwhhhhuuusmith"— Nathan
- I used to believe that the word 'circumstances' was pronounced 'circus dancers'.— Mel
- When i first saw the word "Czech" somewhere, i pronounced it "siz-ETCH" in my head — Pachisu
- When I was little i thought lb for pounds was pronounced lubs, and i called them that for 2 years. Anon
- I used to believe that Off Air was an actual show, possibly about airplanes.— Gretchen
- i used to believe that the world couldn't have possibly started before i was born.— emma