This is 'Floddertje' (messy) and her dog Grease Knees. It is a book about a girl and her dog that can't stay clean for more than half an hour. It is written by Annie MG Schmidt and illustrated by Fiep Westendorp. The book was made into a children's musical and is performed around the Netherlands.
the back reads:
Met de opbrengst uit de verkoop van kaarten en kinderpostzegels steunt Stichting Kinderpostzegels Nederland projecten voor kwetsbare kinderen.
With the proceeds from the sale of cards and stamps, child support Foundation for Children's Welfare Stamps Netherlands projects for vulnerable children.
art by Fiep Westendorp
postmarked in 2011 with a Netherlands 2010 stamp
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Fiep Westendorp (1916 - 2004) was a Dutch illustrator who became especially popular due to her long-term collaboration with writer Annie M.G. Schmidt. The drawings she made for Jip en Janneke, a series of stories which ran in Dutch newspaper Het Parool from 1953 to 1957, now adorn a variety of items sold by a Dutch department store. Since 2007, the University of Amsterdam have an endowed chair for illustration in Westendorp's honor.