Cambridge, Mass.

“PETER AND WENDY,” published 100 years ago this week, famously begins with the words, “All children, except one, grow up.” Like the play on which it was based, the story of Peter Pan captured the rough-and-tumble pleasures of childhood, along with its endless perils and possibilities — the heady “what if?” of imaginative play.

J. M. Barrie’s Neverland, like Lewis Carroll’s Wonderland before it, delivers on the luminous promise of magic, with fairy dust and rainbow water, in a world ablaze with color and expressive energy. Yet the authors of “Peter Pan” and “Alice’s Adventures in Wonderland” also understood that “what if?” had a dark side: the Queen of Hearts ritually demands nearly everyone’s head and Captain Hook repeatedly brandishes his trademark weapon, while a clock ticking inside a crocodile reminds us that time is running out.

These are the traditional villains of children’s books — fabulous monsters with a touch of the absurd. Like Maurice Sendak’s Wild Things and countless others, they walk a fine line between horror and zany eccentricity. They may frighten young readers, but their juvenile antics strip them of any real authority. Alice shrieks with delight when she learns that the Duchess has boxed the Queen’s ears and shouts words like “Nonsense!” to banish threats, while Peter triumphs over a pirate who undermines himself by worrying about “good form” and then resorting to childish practices like biting.

Many authors of more recent books for children and teenagers have similarly crossed over to the dark side, and we applaud them for it. But the savagery we offer children today is more unforgiving than it once was, and the shadows are rarely banished by comic relief. Instead of stories about children who will not grow up, we have stories about children who struggle to survive.

In 2009, Neil Gaiman won the Newbery Medal, the most distinguished award in the field of children’s literature, for “The Graveyard Book,” a work that makes no bones about its subject matter. Here is what children read on Page 1: “There was a hand in the darkness and it held a knife.” A few paragraphs later, the wielder of the knife has finished off three family members and is on his way to the nursery to slash the throat of the fourth. It is up to the hero, Bod — short for Nobody — to find the killer.

These books frequently offer expansive meditations on mortality, with heroes on crusades against death. J. K. Rowling described the Harry Potter books as “largely about death.” The drama of the series begins with the murder of Harry’s parents and turns on an emphatically humorless villain who seeks immortality at any price. Philip Pullman’s trilogy, “His Dark Materials,” takes on similar themes. It rewrites the Fall of Man — instead of being expelled from Paradise, the disobedient, curious heroine seeks redemption by journeying to the desolate Land of the Dead.

But neither the Harry Potter books nor “His Dark Materials” has anything to equal the horrors of what Katniss Everdeen and Peeta Mellark suffer in Suzanne Collins’s wildly successful trilogy, “The Hunger Games.” Katniss must kill to survive in gladiator-like contests, and her victims are not the fabulous monsters of fairy tales or of Wonderland and Neverland, but other children.

It’s hard to imagine Carroll or Barrie coming up with something like that. They were as passionate about their young readers as they were about the books they wrote. In 1856, Carroll purchased a camera with the hope of freezing time through his portraits of little girls. By capturing them in photographs, he made sure they never grew up. “The Boy Castaways of Black Lake Island,” Barrie’s pre-Peter-Pan story and album of photographs, reveals exactly how enthusiastically the distinguished Scottish writer was still playing pirate games after he had turned 40.

The predilections of these two writers for photographing and spending excessive amounts of time with other people’s children may appear suspect to modern sensibilities, but Carroll and Barrie knew what children wanted in their stories precisely because they were so deeply invested in finding ways to win their attention and affection in real life.

These days, few writers spend a lazy summer afternoon taking a boat ride on the Thames with the daughters of a college dean, as Carroll did, or performing tricks with a St. Bernard and telling children stories in a public park, as was Barrie’s habit. Inspiration for many of today’s children’s stories seems to come from not-so-childish sources. For example, according to Ms. Rowling, dementors, those creatures who drain “peace, hope and happiness out of the air around them,” were inspired by her own experience with clinical depression.

Children today get an unprecedented dose of adult reality in their books, sometimes without the redemptive beauty, cathartic humor and healing magic of an earlier time. In “The Hunger Games,” the series that best exemplifies this shift, Neverland and Wonderland have been replaced by Panem, a country built on the ruins of what was North America. In an interview, Ms. Collins traced the origins of the books to her anxieties as a child about the possibility that her father might die while fighting in Vietnam. Then, reading the story of Theseus and the Minotaur, she imagined the horrors of parental powerlessness in the face of child sacrifice. The personal mingled with the mythical, then the banal fused with the tragic. While channel surfing years later, Ms. Collins found herself switching between a “Survivor”-style reality show and footage of young people fighting in a real war zone. The lines blurred, and “The Hunger Games” emerged.

In the trilogy (as in Salman Rushdie’s Booker-Prize-winning “Luka and the Fire of Life,” in which a boy must try to save his father from certain doom), mortal combat takes a video-game-like turn. It’s hard to imagine that we won’t see more books like these, inspired by our shared world of electronic media rather than by the imaginative play of children.

No one is about to slam the brakes on these new engines of storytelling, nor should they. There is much to say in favor of the move to obliterate the divide between books written for children and adult fiction. “There are some themes, some subjects, too large for adult fiction,” Mr. Pullman once declared. “They can only be dealt with adequately in a children’s book.” That insight does much to explain why so many adults can be found browsing books in the children’s section and why books for children and young adults dominate best-seller lists. These writers have successfully produced new literary contact zones for adults and children, with monumental narratives about loss, suffering and redemption.

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.