This is one of my kids' favorite warm-ups:

To the tune of the Mexican Hat Dance:
They're red, they're white, they're brown,
You dig them up underground.
And now there's something new,
They're starting to turn up blue!
Potato, potato, potato, po-
tato, potato, potato, pota-
to, potato, potato, potato,
potato, potato, potato!
Of course, the faster you sing it, the more fun and impossible it is!