The Bunker Diary is the fictional tale of a boy "who's had a lot of problems" and is held hostage in a bunker. Publishers rejected it for 10 years for its "lack of hope".
Brooks said: "There is a school of thought that no matter how dark or difficult a novel is, it should contain at least an element of hope. As readers, children -- and teens in particular -- don't need to be cosseted with artificial hope that there will always be a happy ending."
He had no doubt it would have been published years earlier "if I'd rewritten it -- toned it down, changed the ending, explained a lot of unexplained things -- but that would have meant writing a different book".
Brooks, previously shortlisted for the award on three occasions, added: "I never had any doubts that kids could deal with this, they just have no problem with complex serious stuff."
This is Not My Hat, aimed at kindergarten-age children, tells of a thieving fish who gets his comeuppance. Jon Klassen said that as a storyteller he had to "try to make sure it ends the way the story should end".
"You can do almost anything with kids' books if you do it right," he said. "You don't want to avoid certain plots, you just tell them in a certain way."
- Independent