During World War II, he sometimes assisted Jan Gregoor in forging stamps for the Dutch resistance in identity papers of people in hiding.

[3] A productive commercial artist, his first children's book commission as an illustrator was relatively late in his career, in 1962 for the 10th edition of Versjes die wij nooit vergeten [Rhymes we will never forget].

[4] In 2003, it was adapted as a children's play by David Farmer (Frog in Love), performed by the Tiebreak Theatre Company at Norwich Playhouse.

"[2] Jury president Jeffrey Garrett credited him with fables of human nobility, rather than Aesop's "foolishness, vanity, and meanness".

"The stories of Kikker, or Frog, and his diverse group of friends are miniature morality plays for our age, demonstrating in framed vignettes—as if on a stage—that life can be hard but is in the end good, that there will be comfort: do not give up, do not lose faith, for you are stronger than you think, and you are not alone.