So I take my (much-read and much-beloved yet pristine, purchased as an adult,) copy off the shelf, where it is tucked in between Outside Over There and The Nutcracker, and look it up -- the line really is "let the wild rumpus start"?
Yet a quick google confirms I'm not the only one who misremembers it, and some people are quite vehement in their inaccuracy.
So, I've decided it's like the line "play it again, Sam."
(Or the disregarded double dots in Be Not Afraid?)
(Ah! BITE YOUR TONGUE!!!!! how DURST thou put that in the same category as Casablanca? or even the merest thoughtless and discarded doodle of Sendak??!?#?$???)
The collective memory has corrected the creator's minor misstep. The rhythm is better, (especially if you shout it, and really, why wouldn't you?)
Let the Wild Rumpus Begin!
(Incidentally, I didn't hear him say them, but in retrospect, the celebrant may have accidentally uttered those words at a Mass I attended recently, instead of "let us being in the name of the...," at least judging from the activity that followed.)