I used to believe that dogs from other countries had different languages. So a dog raised in Japan wouldnt be able to understand the barking of an American dog. Actually, that still sounds kind of plausible to me...
A childhood belief about cats and dogs

others believed things like this
- When I was little I used to believe that dogs talked to each other when barking.Anon
- when I was a child I used to believe...that dogs barking at night were chating about their day job.— Ronald Sanchez
- At the age of four I believed I was soooo smart. I spoke TWO languages...English AND American!— Melinda
- I thought Oklahoma was a place in Japan (due to it weird name :P), and Japan gave it to USA later.— Luiz Alfonso
- I was shocked when I found out that dogs in foreign countries didn't know English commands.Anon
- I used to think dogs had hooves, because they make hoofbeat-like sounds when they walk.— Samuel Lamont