As well as Dutch and Flemish titles (only to be expected) the list already contains the likes of Charlotte's Web and The Cat in the Hat, Where the Wild Things Are and The Snowman.
I take it their definition of "beautiful" is as wide as can be, since they include not only Sendak and Briggs, but also books like Harry Potter and the Philosopher's Stone, which as far as a recall didn't have a lot of beautiful illustrations, if indeed it had any.
So let me throw the question open to readers: What do you think is the most beautiful children's book of all time?
Already noted:
Beatrix Potter all
The BFG
Charlie and the Chocolate Factory
Alice in Wonderland
Le petit prince
Tracy Beaker
Matilda
Narnia
Pippi Longstocking
Guess How Much I
Winnie the Pooh
Vote in comments, as often as you like.