Rolf Zuckowski's song "Und ganz doll mich" at least some years ago was the respective entry at the Guinness book with 3776 lines all written by children. I don't know whether he has ever recorded the full length version. He's popular in Germany, though not with me.

The Devil Glitch" by Chris Butler is the longest pop song recorded according to the Guinness book with 69 min.

Wolfgang