This is an issue close to my heart, and I'm going to take a moment to discuss it. At least in brief (as brief as I can be about it).
"Still, it is hard not to mourn the decline of the literary tradition invented by Carroll and Barrie, for they also bridged generational divides. No other writers more fully entered the imaginative worlds of children — where danger is balanced by enchantment — and reproduced their magic on the page. In today’s stories, those safety zones are rapidly vanishing as adult anxieties edge out childhood fantasy." -- No More Adventures In Wonderland, by Maria Tatar, New York Times, October 9, 2011.
This person wasn't necessarily attacking the modern trends as just commenting on them, but I do think her entire approach to the topic is very narrow.
Ultimately, it is not "children's books" that are turning "dark." It is "young adult" fiction that is starting to diversify, shucking off the restrictions and scorn of society when it comes to including themes such as abuse, violence or sexuality. Many, including myself, say that's a change for the better.
Young adult fiction is read by a wide variety of ages - I'm a fan of Harry Potter, Artemis Fowl by Eoin Colfer, and The Shadow Children by Margaret Haddix, and I'm well out of high-school. The idea that young readers, those from 10-25 years of age, should be restricted to only certain themes and tones in their books, or that certain themes and tones are "depraved" and inapplicable, is quite foolish and ignorant of the massive age-group in question.
Not only do many authors maintain that tradition of humor and enchantment, including Harry Potter, but the belief that today's youths would be content with insipid, low-stakes, "flights of fancy" is just ludicrous. Again, to use Rowling's magnum opus as an example: the books were intended to mature along with the audience, and you may have noticed Harry Potter was a huge success, keeping up with the target audience's interests nicely. If you think fourteen- or eighteen-year-olds are going to want the same sort of literature as children much younger than they are, then you don't understand how to write for children. I actually found the Harry Potter books quite childish and irritating at first; I didn't want to hear about "snitches" and "whomping willows." Apparently, I was the target demographic, so there you go.
The diversity between children within a single year of age, let alone the entire spectrum designated as "young adult readers", is staggering. It is absolutely essential to differentiate between the books intended for young children and those intended for an older, albeit youthful, audience. Are we truly seeing a pandemic of dark, brutal themes in children's books or are the critics confusing tweens and teens for vapid young children? To treat them all as the same, assuming they all want to read the same things for the same reasons, is simply incorrect - as is the belief that childish wonder and imagination isn't present or titillated by contemporary young fiction.
I applaud Maria Tatar for admitting that the lines between child and adult are blurry (they always have been - especially when you actually mean "young-adult" instead of "four-year-old toddler) and that the subsequent blurring of their themes in fiction is not all that bad. However, I feel there is no need for concern. Modern fiction is not wandering down the darkened alleys to be forever lost to "adult" anxiety and monsters, something which I do agree would be tragic. Speaking of that...
Regarding why Rowling came up with the Dementors - ostensibly due to her experiences with depression - how does that affect the young readers? What does it matter? Beyond that, why would "depression" be such an alien, or unwanted theme when it came to young-adults? No fourteen-year-olds have ever been depressed themselves? This is just one example - do you truly think a young boy has never been afraid of war? Of disease? Of disaster? Or felt the bitter frustration of poverty? None of these "adult anxieties" are as foreign and inapplicable to children's/young-adults' fiction, or real experiences, as these sheltered critics believe.
Besides even that, youths, particularly those over the age of ten, thrive on melodrama. They love it in all its forms. Protecting twelve-year-olds from drama is not wanted by them (they can regulate their own reading experiences anyway) nor is it beneficial.
I cringe whenever I see self-righteous "critics" of contemporary youth literature, and indeed, of other media for youths, dictating what themes should be acceptable for this audience when they clearly have not even thought to ask that audience what they feel about it, let alone truly come to understand them. Are the young readers, from ten to twenty-five, of the world not pleased with the tales brought to them by the likes of Rowling, Colfer, Haddix, Tamora Pierce, Tolkien, Eddings and other fantastic authors? Do they not find their imaginations taking flight? How many of them are instead picking up JM Barrie's Peter and Wendy? How many have ever said: "I can never find a story that suits my reading ability and doesn't make me upset because it's so dark?" Contemporary children's fiction does indeed balance enchantment and danger, and one shouldn't assume that the only way to reach out to children in writing is to "recreate" the worlds of their imagination.
Oh, but what if they have been through these horrors themselves? These dark themes and experiences? Well, I'll let someone more accomplished than I take it from here. Though not before pointing out that this, too, is idiotic - and that, you know, kids and teens can moderate their own reading experience.
Stop underestimating them and their experiences, and for the love all, don't advocate that we make reading even more distasteful to youths by flooding future libraries with insipid pap with the dramatic weight of a Parisian street-mime.
* - Yes, Tolkien wrote for children. Some would consider "The Lord of The Rings", and the fantasy genre itself, to be mostly for young readers. Yes, even, say, Feist's work, which mentions child sex-slavery and wanton murder. These topics don't faze seventeen-year-olds. Come to mention it, there's mention of child sex-slavery in David Eddings' The Tamuli, and more killing than there was punctuation. Loved that trilogy when I was thirteen.
Banned Book Week may be over, but the fight against the beige-wearing, religiously-blinkered moral interferers that want to tell you and your children how to think and feel isn't won yet, folks.