Bismillahir Rahman ir Rahim -- when I was a kid in the 80's I believed (along with a lot of adults, I suspect) that the "cola wars" were terribly serious. I imagined a nation divided in vicious opposition between two warring soft-drink superpowers, and followed developments anxiously, fearful that any day one would crush the other utterly and rise victorious to reign over all Americans with its tyrannical single-soda regime.
A childhood belief about adverts

others believed things like this
- I thought that soda was also called "pop" because if you drink too much of it, you'd explodeAnon
- I thought there was a legal drinking age for soda (I had always been told that soda was not for children).— Dial Zero
- Because of Pocahontas, I grew up believing Native Americans noises sounded like English to Native Americans.Anon
- I used to believe that it was the Star Wars "Tri-ology" instead of the Stars Wars "trilogy".— keith Key
- I once believed that Tusken Raiders from Star Wars Where a Type of Demon like Satan in the BibleAnon
- Follow me and I will make you vicious old men.....OOPS that was really fishers of men— oddsox