I get books from the library for our kids. My general rule is the book has to be published before 1970 to be worthwhile. We read newer books, like Pseudonymous Bosch's Secret Series and Joshua Lacey's Grk books, but they're like watching episodes of The Fall Guy or eating peanut butter fudge: highly entertaining, but detrimental in excess. Right now I'm reading The Bronze Bow (Elizabeth George Speare's 1962 Newbery Medal winner) with Articulate Joe and The Long Way Home by Margot Benary-Isbert (1959) to all three of the older kids.
What's wrong with modern children's books? They seek to validate rather than shape. They're full of characters "just like you!" who learn that it's "okay" to be just like you. If the characters have opinions about anything, they tend to learn that other opinions are just as valid. But Speare's Daniel learns that his disappointment in the teachings of Jesus is his own problem, and Benary-Isbert's Christoph experiences the oppression of statism in a real-life state, not in Panem. These books teach the superiority of Christian humility and pacifism to the state of war, and of individual liberty to collectivism.
I understand that kids with troubles need to see others experiencing those same troubles and overcoming them. That's helpful. But it seems like you can't get a children's book published today unless the main character is being abused or suffering from a psychosis. Even modern books that hint at dealing with deeper material (such as the Secret Series's dealing with the purpose of life) ends with meaningless platitudes; I maintain that there is supposed to be more to life than "getting to the other side," and on some level the novels function as a kiddie primer on existential-angst-cum-nihilism with their core theme that the "secret to life" is a joke.