Mr Gum and the Dancing Bear won the prize for 7-14 year-olds
Tales of a witch's children and a "mean, cruel, smelly and ruthless" man called Mr Gum have won the first Roald Dahl Funny Prize for children's novels.
Ursula Jones's The Witch's Children Go To School and Andy Stanton's Mr Gum and The Dancing Bear were named winners by children's laureate Michael Rosen.
Rosen led the judges, who included Dahl's granddaughter, author Sophie.
Comic Dara O'Briain, author Kaye Umansky and cartoonist Chris Riddell completed the panel.
Rosen called The Witch's Children Go To School, illustrated by Russell Ayto, "a rumbustious tale in the tradition of mischievous spirits causing mayhem and disorder where it's least wanted".
"Every page shouts with the sound of chaos and surprise," he said of the book, which won the prize for children aged six and under.
Mr Gum and the Dancing Bear, illustrated by David Tazzyman, took the award for children aged seven to 14.
The author, who was thrown out of Oxford University, wrote the first Mr Gum book as a gift for his cousins, "to make them laugh," he has said.
"It is everything the Roald Dahl Funny Prize was invented for," said Sophie Dahl, calling it "quirky, odd and deliciously funny".
Roald Dahl, who died in 1990, wrote a wide range of fiction, but remains best known for children's works including James and The Giant Peach, Charlie and the Chocolate Factory and the BFG.
In 2005, a museum dedicated to him opened in Great Missenden, Buckinghamshire, where Dahl wrote many of his best-known works.
The Roald Dahl Funny Prize was created by Booktrust, the charity behind the Orange Prize for Fiction and other initiatives to promote reading.