Until 8 years old I thought that different countries that we visited during long evening airline flights were actually different planets. This explained why certain places were much hotter/colder than others (tropical Asia were Mercury or Venus closer to the Sun, while Northern Europe was Saturn.)
A childhood belief about places

others believed things like this
- I used to believe that the moon was another country and that all countries were little planets.Anon
- I thought venus fly traps are from the planet Venus— Ted Snow
- For many years I didn't understand why everyone was talking about the 'youth in Asia' (euthanasia).Anon
- I used to believe that ketchup was used to make fries colder so they would be easier to eat.— Amber
- I used to beleive Freddy Mercury was a wrestler— Owain
- My mom thought "euthenasia" meant Asian kids.(youth in Asia)— Ibelievedher!