On the other hand, just to hedge my bets, Salty makes an extremely good point in saying:
It wasn't me who said that
Reporter confusing Cabin Essence for Child if Dennis played or mentioned both sounds plausible to me, that's the way I've always read it. Of course the "this is the prayer I'm working on for it" comment is just bizarre without context in either scenario.
I believe those Worms lyrics were known about in some capacity from a 1997 issue of ESQ, if not even earlier. I don't think they were fully transcribed. As far as I know they had access to Frank's original lyric sheets, handwritten by himself and Van, which only included the songs he did illustrations for - Heroes and Villains, Surf's Up, Do You Like Worms, Cabin Essence.
"My vega-tables" - The Elements came from a conversation with Van Dyke about the concept rather than anything written down.
There ain't much in the Inside Pop reel notes to support anything about Child lyrics, it just says:
1. hands to face CR angle
can't see hands pan to hands in dark
child Is the Father of man
2. Heroes & Villains plays
Vandyke Parks has been working on lyrics
sings open country song
Not that it matters, but the group vocals it describes them working on appear to be the Wonderful yodelling, the Cabin Essence verse doings and re-recording the 'iron horse' chant, no Surf's Up 'til Brian does it alone.