Thanks to my friend CLM for pointing the way to this children's picture book on the Astaires, which was published last September.
FOOTWORK was written by Roxane Orgill and illustrated by Stephane Jorisch. It's aimed at the 4- to 8-year-old set. An unusual -- but most welcome -- topic for preschoolers and beginning readers.
I'll be looking for this so I can browse through it the next time I'm at a bookstore.