I Want My Hat Back
This Is Not My Hat
We Found A Hat
The Rock From The Sky
They're beautiful exercises in minimal, precision watercolor. They're written with delightful economy, and have a rather Dahlian sense of justice and consequences.
He wrote them all within the last twelve years, IIRC.
For older kids, Pax (illustrated by Mr. Klassen in the edition we picked up) is a lovely piece of writing, vaguely like a cross between My Side Of The Mountain and Old Yeller, but less tragic than Old Yeller, with a deftly-handled thread about emotional awareness and responsibility for one's own choices woven throughout.
Oh, and the How To Train Your Dragon books, by Cressida Cowell, are wonderful, hilarious pieces of work about self-discovery, loyalty, friendship, and the hard, slow struggle to achieve mastery and skill in a world where people expect you to be something rather different than you are. Vastly, vastly better than the popular movies loosely inspired by them, and quite different - closer to a child-friendly Hitchhiker's Guide than the Hero's Journey of the films.
Great new classics are still being written - it's just that the winnowing function of passing decades hasn't yet run its course, so they're harder to find.
This is true, but I also think there are 'golden ages' for various genres of literature and I suspect we are not in a golden age for children's literature right now.