Also, I wrote a 900 word review of Brown Bear, Brown Bear analyzing it's subverisve warning about today's surveillance state. Pretty proud of that one.
My contribution to the discussion would be The Bear Snores On. Some great phrases in there that keep it interesting enough that I don't mind reading it 3 times a day, yet fun enough the little guy still enjoys it.
Even better than the book is Samuel L Jackson narrating it: https://www.youtube.com/watch?v=nDGKK6y8OtQ
It probably would have been my favorite! Just kidding. Maybe?
For younger children, I'd say The Wind in the Willows.
I think it depends on age - my wife and her friends are teachers, and they think the most important thing is to learn the structure of language, and rhyming is an important part of that. They always recommend Julia Donaldsons books like the Grufalo, and Jack and The Flum Flum Tree for younger ones
If it's a book for young children (the kind that parents are going to read to them, and therefore have to read over and over), you need to make it not a bore for the parents. Maybe the best example I've seen is "The Bravest Ever Bear".
Anything by Verne
Tom Poes (but you'd need to read dutch for that)
Master of the black mill (Krabat) (Harry Potter, but different and much older)
Also Robert Munsch's Love You Forever. Warning, make sure tissues are nearby: https://www.youtube.com/watch?v=6z-oBkgJ4Ow