I used to think that "stretch marks" were those lines that you get on your tummy when your jeans are too tight.
I remember being about 8 and saying "Gosh mom, you sure have a lot of stretch marks on your stomach!" and getting slapped like 3 feet across the room.
A childhood belief about skin

others believed things like this
- I thought that exclamation marks were actually "explanation marks", since they explain how you pronounce it.— superoid
- I used to believe that you could stretch a rat's body to be super long.Anon
- I used to believe that beauty marks (freckels) were Butterfly bites!— Jolene
- The song "Reverend Blue Jeans" turned out to be "Forever in Blue Jeans." Who would have believed that?— music lover
- I thought the "physically fit" lines in the song "I Like to Move It" were "fizzy coloured feet".Anon
- I thought cartoons were real, I remember asking my mom why there were lines around the "actors" in a cartoon.— Steven Graziano