I don't understand the words he's singing but how can you not think this is adorable?
Something about "My mom sang this song. It isn't very pretty, it isn't very long" blahblahblah
Then "Pigs don't live in houses and pigs don't make their beds.."
I do know it's a song that he learned at church, about the difference between you and a pig. About how you, being the human, should be clean and neat, not like a pig, which is an animal.
If you listen closely, you can hear Josie doing her lovely yelling/banshee screaming thing in the back ground. In clear contrast to Jarrett's cute performance.