De zwarte donuts:
"De Zwarte Donuts op Zwemles" (The Black Donuts take Swimming Lessons) is a children's book written by Joan van den Hengel.
It follows a band of comical motor riders on their quest to earn their swimming diploma. Hilarity ensues on the way there and in the swimming pool, as they come to realize their tough-guy personas don't mean much when you can't swim!
For the children who like their humour to be a bit more dirtier than in other children's books!