The above post is correct.
The young boy is named DIXON. His father is "The Worm."
Dixon's rap goes as follows:
Check that ego -- come off it -
I'm the prophet -- the professor -
Ima teach you 'bout The Worm -
Who eventually turned to catch wreck
with the neck of a long time oppressor
And he's runnin from the devil, but the
debt is always gaining
And if he's worth being hurt, he's worth
bringin' pain in -
When the sunshine don't work, the Good Lord
bring the rain in.
http://www.imdb.com/title/tt0175880/alternateversions
http://www.imsdb.com/scripts/Magnolia.html