From the song Rain, Rain, Go Away mentioned above a pain relief company had an ad campaign that said pain, pain, go away come back another day otherwise, I agree with the others concerning what a mother would say and do by kissing.
Thanks, everyone! One of my friends residing in the U.K. says she often hears children, including her kids, whisper 'Pain, pain, go away, come back another day.' Would it be regional? She lives near Cambridge.
She says people in her neighborhood sings it to alleviate a kid's pain when he/she has fallen down and has a 'boo-boo.' Kind of like a magic to push it away. She says it's very popular amongst children.
Anything is possible in a speech community. I’ve never heard kids do it. Obviously your friend lives in a place where a parent has said this enough to make it a pattern around her. It’s very possible that any number of individual people could come up with this little ditty and then it could spread out around them.