When John was young, his father played the ukulele and sang songs John thought his dad had written, but which turned out to merely be old favorites (such as “Seven Old Ladies Stuck In A Lavatory.” )
The opposite has happened to my kids. John has made up additional lyrics to songs that my kids have no idea are not part of the original. (Such as “he bumped his knee and went to tea” as a second verse for “It’s raining, its pouring, the old man is snoring.”)
On a completely different note, I just got to use the phrase: “I saw the mouse’s pants go by.” How often do you get to say something like that?