I used to believe that former Washington, DC mayor Marion Barry was two people, Mary and Barry...and Mary was his wife. When I was 10 I saw it spelled out on the news and finally realized it was just one person.
A childhood belief about names

others believed things like this
- I used to think that the title of Barry Manilow's song "Looks Like We Made It" was "Looks Like Tomatoes".— close2nd
- I used to think virgin mary was actually 'virginia mary'Anon
- I thought "Virgin Mary" was actually "Verge 'n Mary" and that Verge was a nickname for Joseph. — Rachel
- I used to think my grandma was THE Mary Poppins.Anon
- when I was about six I remember asking an Adult what Mary did before she was a statue....Anon
- When I was 3 I was convinced that I would mary John Bon Jovie— Jessie