I believed that when girls got older they no longer had the time to go to the bathroom (I'm sure an assumption based on the tampon commercials with ladies proclaiming a need to accomodate their busy lifestyles). Tampons and pads were the evolution of the diapers.
A childhood belief about periods

others believed things like this
- I used to believe that tampons were diapers for girls because they can't control when they pee...— Tien
- I used to belive ( along time ago) that the pads my mom used were diapers for mummies.— Kristie
- I used to think that pads were little diapers for my baby dolls.. haha— Lalala
- i used to belief that tampons were rolled up pads in a tubeAnon
- Adult diapers feel and sound just like baby diapers but dont have the cool prints on them— jakjflkaj
- I used to think that tampons were meant to absorb women's urine so they wouldn't have to go to the bathroom.— Koyaanisqatsi