Certainly everyone has some embarrassing things they thought were true as a kid. Me, I thought that chipmunks were baby squirrels. A recent 2ch forum thread (later rounded up and commented on at Itashin!) took up this at times awkward topic and we selected 10 particularly cute ones. Note that our highlights are mostly skewed toward things that seemed unique or particularly Japanese (e.g. not Santa, although he came up). Please remember that since it was just a forum conversation, these are not necessarily widespread beliefs.
When I was little I thought (paraphrased from Japanese)