When a wunderkind comes trading on his own wide-eyed innocence, people naturally cry foul. Although Jonathan Safran Foer’s “Everything Is Illuminated” was a success in every way, critics called it precious. Mr. Foer’s sensibility is drawn to tragedy – the Shoah in his first book, the attack on the World Trade Center in his new one, “Extremely Loud and Incredibly Close” (Houghton Mifflin, 368 pages, $24.95). These traumas create, for Mr. Foer’s characters, a bubble in which innocent goodwill is preserved in a way most mere mortals distrust, and perhaps envy.

Mr. Foer sidesteps some questions here by making the hero of his new novel an actual child, and a very precocious one. Oskar Schell’s name alludes to Oskar Matzerath, the similarly traumatized, but darker and more streetwise hero of “The Tin Drum.” The magical realism of that novel, and of Mr. Foer’s first, is here contained in Oskar Schell’s “inventions.” Whenever he feels troubled, Oskar asks, “What about a googolplex telephone? What about safety nets everywhere?”

Oskar’s father was killed in the towers, and Oskar’s fantasies operate at the resolutely municipal level of the imagination that New York enjoyed in the wake of what Oskar calls “the worst day.” The archival impulse, so prevalent in contemporary art, plays on the transmogrifying power of scale: Tears, in great civic quantities, become triumphal; touches, sewn into a quilt, become sad. How to mourn a personal loss within a public tragedy? Which standpoint, lyric or civic, is right?

Oskar, who is obsessed with Stephen Hawking’s “A Brief History of Time,” does not scruple with scale. He presumes that his emotional wiring is compatible at a citywide scale, and undertakes a real-life project to match the grand optimism of his “inventions.” After he finds a mysterious key labeled “Black” in his father’s closet, he tries to systematically meet everyone named Black in the city.

Today’s New York looks pretty rosy through Oskar’s eyes: Almost everyone is preoccupied, but ready to be touched by Oskar’s forthright goodness. Pride, for better or for worse, does not seem to exist in this novel. But these adventures are instantly compelling – whatever the value of Mr. Foer’s attitudes, his writing is quick and rich. He is at his best when filtering realism through a whimsical idiolect like Oskar’s, or like that of Alex Perchov in “Everything Is Illuminated.”

Oskar’s adventures are interspersed with weaker, epistolary fragments written by Oskar’s grandmother and grandfather, who emigrated to New York after the fire-bombing of Dresden. Oskar’s grandmother writes “Sometimes I imagine stitching all of our little touches together. How many hundreds of thousands of fingers brushing against each other does it take to make love?” In other words, she, rather disappointingly, has precisely the same sensibility as Oskar.

These sections allow for too many textual hijinks; the page-long ellipses that featured as a climax in “Everything Is Illuminated” are replaced here by photographs and other expensive printing tricks that, though nicely decontextualizing, are more than anything reminders of Mr. Foer’s commercial success. They are also part of Mr. Foer’s general interest in the pathos of miscommunication. In his previous book, the supernaturally forgetful Yankel has to write notes on his wall in order to remind himself who he loves; here, Oskar’s grandfather loses the power of speech after Dresden and resorts to writing out his half of conversations. In Mr. Foer’s worlds people become close because they are far apart, because they can’t understand one another, or are different ages, or are refugees. Suffering is the opportunity for feeling.

Oskar, in a mood of proud complaint, tells his shrink that “I’m constantly emotional.” Tragedy gives Oskar the key to the city, enhancing his childish narcissism. He keeps a diary titled “How I Feel Now,” in which he crosses out “Mediocre,” writes “Optimistic, but Realistic,” and then crosses that out to write “Extremely Depressed.” In these tenuous moments, Mr. Foer seems comfortable with an innocent’s lack of emotional sophistication. And his hand-in-glove relation of meaningfulness to tragedy can feel manipulative.

It is hard to write a novel without having an idea. “Extremely Loud and Incredibly Close” is not as good as “Everything Is Illuminated,” but it is based on the same idea, and it is for this idea that Mr. Foer can be criticized. Mr. Foer clearly has great faith in the art of the novel, and is ready to use it to treat the touchiest subjects possible. But he is writing against the grain of American novels, so often agents of self-conscious maturity. Mr. Foer has a different idea, refusing to make a proof of experience, or frown, or wink, or to write about self-consciousness in the normal manner at all.