The notion that kids grow up too fast these days is a complaint so familiar that it can seem both true and meaningless at the same time. It has the status of received wisdom, and received wisdom doesn't usually inspire anybody to make the case for it. You may as well present a detailed brief for why it's not the heat, it's the humidity.

In "Ready or Not: Why Treating Children as Small Adults Endangers Their Future -- and Ours," Kay S. Hymowitz, a senior fellow at the Manhattan Institute, bothers to make the case. Though the Manhattan Institute is known for its conservative agenda, the argument here is nuanced enough and politically balanced enough for neither left nor right to dismiss.

Over the past 30 years or so, Hymowitz believes, we have gradually been undermining the traditional notion of childhood as a period of protection and apprenticeship, during which adults provide moral guidance to the young. From roughly the mid-19th century to the mid-20th, Americans embraced what Hymowitz calls the doctrine of republican childhood, a bundle of ideas about child rearing that included the rejection of corporal punishment and the encouragement of free play -- along with the presumption that the child had to be actively molded by adults into "the independent moral actor demanded by a free society." By now, though, the old ideology has given way to one both harder to define and more pervasive -- one in which warmed-over Romantic notions of the child as a naturally moral creature, faddish educational schemes that seem to call for teaching children only what they think they want to know, and even the kind of sophisticated marketing that seeks to turn toddlers into consumers all combine to render adult authority ever more wobbly and children more autonomous.

These days, Hymowitz argues, too many of us are inclined to see children as rational, independent, self-motivated miniature adults who know better than their elders what they need and want. Adults, meanwhile, define themselves as childen's allies, partners and friends, whose role is to "empower children, advocate for them, boost their self-esteem, respect their rights and provide them with information with which they can make their own decisions."

The proponents of such thinking are, in Hymowitz's view, many and varied, beginning with the experts who advance the fashionable notion of babies as learning machines, so efficiently pre-programmed to lay down neural pathways that parents can seem expendable to the process -- except insofar as they supply brain-building Mozart and black-and-white "infant development toys." Then there are the educational theorists who cheerlead for "child-centered" learning, in which teachers are demoted to "co-learners" or "managers of instruction." And there are the conservatives who want to overturn the entire system of juvenile justice and try 11-year-olds as adults. The list goes on: marketers who have ensured that many American children make brand decisions by the age of 4, advertisers who have transformed the 8-to-12-year-old population into a lucrative market known as "tweens," television executives who have lured the previously untapped 2-and-under set to the tube with candy-colored shows like "Teletubbies."

This may seem like an awfully diverse crew of culprits -- like Reds under the bed, the childhood snatchers are all around us. And it's true that Hymowitz stretches her thesis just about as far as it will go. But if that's a weakness of "Ready or Not," it's also a strength. The fact that Hymowitz implicates not only the usual suspects for social conservatives -- sex ed instructors, avant-garde educators -- but also, for example, corporate marketers, makes her argument far more resonant and less tendentious than it might have been. (Indeed, she is at her most eloquent when writing about the false promise of freedom from adult strictures that advertising seems to promise: "The rise of the child consumer and the the child market itself is compelling evidence that children will always seek out some authority for rules about how to dress, talk and act.")

With all this to recommend it, "Ready or Not" nonetheless leaves itself open to plenty of argument. A book as reliant as this one is on secondary sources -- child-rearing advice books, education textbooks, articles culled from newspapers and magazines -- inevitably makes you wonder about the gap between theory and practice. Parents may buy books about the self-regulating baby and the inherently rational child, but that doesn't mean that in the actual world of colic and tantrums they treat their kids as theoretical models sprung to life. In general, the facts of family life interest Hymowitz less than theories about it do. There's something to be said for that perspective, since the demographic side of this story -- overworked two-career couples, children and adolescents more isolated from adult company than they once were -- is by now familiar. But Hymowitz never bothers to acknowledge that theories and doctrines aren't transported whole into homes or schools, and she supplies little in the way of reporting from the field.

Sometimes this neglect of the facts on the ground hampers her argument considerably. She complains, for instance, that American adults are shirking their duty to the young by perpetuating their own adolescence -- marrying later, lingering in college and job-hopping. There is some truth to this, but Hymowitz doesn't even mention the fact that life cycles have changed. Americans live longer than they did even 30 years ago, and considerably longer than they did in the last century, which means that, for example, a woman who marries at the age of 25 stands a good chance of being married longer than her grandmother or great-grandmother who married at 18. Besides, unlike Hymowitz, I can't see that the options of marrying later, switching careers or prolonging one's education are signs of cultural decline.

Still, she has produced a book worth debating. Since reading it, I've been looking at the world through her thesis, detecting evidence for (and against) it in all kinds of cultural phenomena. For any work of social criticism, that's praise indeed.