I told my wife recently that she was singing the nursery rhyme 'Pat-a-cake' to my daughter wrong - She kept singing "Pat it and prick it ad mark it with 'B'...".
As my brother's name and my name both begin with 'S' I was convinced until recently that our Mum always sang the line correctly ie "mark it with 'S'.."
I am now 31 and find it amazing that I had this belief ever since I was a child!.
A childhood belief about misheard lyrics

others believed things like this
- I used to belief that the birth mark on my dad's leg was where he spilled his coffee... EVERY morning.— Liz
- My daughter thought Paul McCartney was singing "Hey Dude" instead of "Hey Jude". Anon
- I used to think that pepper was only used to mark where you'd put the salt.— BK
- I used to believe that my birth mark was a tea stain!Anon
- I used to believe that everytime a balloon was released , it meant that a child had recently died.— Samantha
- When i was little i used to think that a birth mark was the place on the body where you came out of the mother— bipbop