Paul Lukas, of Uni Watch fame forwarded this awesome illustration to me. (Best children's book illustration ever? Quite possibly," he says.) He in turn got it from a friend.
It appears to be from some sort of 1946 promo of a book yet to be published at the time. I can't find any mention on the web of Peter and the Moon in connection to Jan Balet, so who's to say if it ever appeared on shelves—or is so far out of print that it doesn't appear online. Balet appears to have hit his stride in the late 1940s.