It’s always gratifying to hear a new twist on an old joke. In the Marx Brothers’ “Duck Soup,” Rufus T. Firefly, played by Groucho, is handed the Freedonia cabinet’s treasury report: “Why, a child of 4 could understand this report. Run out and find me a 4-year-old child — I can’t make head or tail of it.” Alison Gopnik, a professor of psychology at the University of California, Berkeley, has run out and found plenty of 4-year-old children. In her new book, she announces that they are in some ways “smarter, more imaginative, more caring and even more conscious than adults are.”

Gopnik does not go so far as to propose that we fire Timothy Geithner and march in a phalanx of preschoolers to fix the credit crunch. She does, however, make the bold suggestion that thinking about small children can shed new light on ancient philosophical problems. Whether or not this is true, her account of what the science of recent decades has had to say about infants’ minds tells a fascinating story of how we become the grown-ups that we are.

Early childhood is both familiar and mysterious. Everyone was a baby once, and most adults have spent plenty of time talking to small children. But we simply can’t remember what it was like to be younger than 5 or 6, and conversation between an adult and a preschool child is far from a dialogue between equals. Our mental development is, Gopnik argues, more like a metamorphosis than an incremental process of growth, so we butterflies can boast precious little understanding of the caterpillars in our strollers. To see what is really happening in their heads, we need grown-up science, in the form of cunningly designed and rigorously executed experiments — supplemented, where possible, with brain scans.

Thanks to such work, it seems we can now get over some of the false or misleading ideas about childhood inherited from Sigmund Freud and Jean Piaget, the pioneer of developmental psychology. They maintained, for example, that small children cannot discriminate between truth and fiction — a verdict with which it is all too easy to concur when you have just been informed by a pint-size superhero in a cape that there is a fire-breathing dinosaur in the laundry basket. But it turns out that even 2- and 3-year-olds are very good at telling pretence from reality. The experiments described by Gopnik are pretty convincing on this point (though here and elsewhere in her book it would have been interesting to hear more about how exactly Freud and Piaget managed to go so wrong).

When children are playing, they know they are just playing. Yet play is a very serious business, as Montaigne recognized: without the luxury of a uniquely long period of dependence on adults, in which we can afford to explore the world with unfettered imaginations, we would never learn how to be the most knowledgeable and powerful creatures on the planet. A recurring theme of Gopnik’s is the idea that playful immersion in freely conjured hypothetical worlds is what teaches us how to make sense of the real one. She describes, for instance, how small children’s grasp of “counterfactual” situations enables them to calculate the probabilities of alternative courses of action. She also discusses the invisible friends — most often found in the imaginations of children between the ages of 2 and 6 — who seem to help youngsters learn how to interpret the actions of others. Children who have imaginary friends tend to be better at predicting the thoughts and feelings of actual people. Autistic children almost never create imaginary friends or engage in any kind of pretend play.

It used to be held that small children are not only irrational but also immoral and egotistical. Again, we may have been doing them an injustice. The notion that moral ideas develop only in adolescence — as Piaget, for one, claimed — appears to be wrong. Even children as young as 2 can grasp the difference between moral rules, which are intended to avoid harm (“Don’t hurt other kids”), and merely convenient regulations (“Take off your dirty shoes at the door”). Tellingly, small children recognize that it would not be O.K. to hurt another child even if a teacher said it was. This does not, of course, prevent the little devils from lashing out on occasion, but such bad behavior seems to be a matter of undeveloped self-control rather than a psychopathic lack of moral concepts. In a section that is heartening news for optimists about the human race, Gopnik reports that children are naturally empathetic from birth and tend to exhibit altruism (though fitfully) from the age of 1.

In the 1980s and ’90s, Gareth Matthews, a professor of philosophy at the University of Massachusetts, Amherst, made an impressive case for regarding young children as natural-born philosophers. Matthews illustrated how much their open-ended intellectual curiosity has in common with the apparently aimless ruminations of professionals — thus, in effect, painting adult philosophy as a form of arrested development. Gopnik’s surprising claim about the importance of children to philosophy is not that they ask the same questions as grown-up professors (she does not in fact mention Matthews’s work), but that thinking about children can somehow provide the answers the professors are looking for.

When Socrates pondered the immortality of the soul, Gopnik argues, he should have considered the sort of afterlife that parents can obtain through their children. Similarly, she thinks moral philosophers ought to take greater cognizance of the empathetic bonds between generations, and that those skeptics who wonder how we can ever attain certain knowledge of the outside world would do well to consider the mechanisms by which children learn. As for the meaning of life, readers will not be surprised to hear that Gopnik suggests a large part of the answer is (if you have them): children.

Nearly all the great philosophers have been men, and Gopnik claims that this helps to explain why the nature of children’s minds has almost never been discussed in philosophy. But there is an alternative explanation: perhaps children have been left out simply because they are on the whole not all that relevant. Although many philosophers have been childless men, not all were — Descartes developed a strong bond with his daughter — and Bertrand Russell ran a school. Are we really to suppose that merely being male has blinded philosophers to the gold that has been lying at their feet? Gopnik’s exposition of philosophical problems is sometimes sketchy, and in the absence of more solid examples of missed great ideas than she provides here, I am not convinced that the history of philosophy would have found more useful inspiration from the study of children if only its luminaries had included Mrs. Plato, Emmanuelle Kant, Renata Descartes and Joan Locke.

Gopnik notes that parenting in today’s middle-class America is unusual, because comparatively few people are involved in the care of each child and so parents are more intensely involved in it. Extended family, older siblings and neighbors play a smaller role than they did in the past and elsewhere. She interestingly suggests that this shift helps to explain why many American parents now make such a song and dance about the formerly unremarkable activity of child-rearing. One might go further and regard our absorption in our own offspring as a flimsily disguised form of narcissism. Either way, the notion that children’s minds have much to tell us about the meaning of life seems rather a fond exaggeration.

Anthony Gottlieb is the author of “The Dream of Reason: A History of Philosophy From the Greeks to the Renaissance.”