Madame Bovary is not a slut.

Little Children references Flaubert's Madame Bovary at great length during a book group discussion attended by the film's protagonist, and it's easy to see how Flaubert's conflicted heroine is mirrored in Winslet's character. But it's also a clue about the fragile, often paradoxical tone of the film; Flaubert's work is characterized by the conflict between romanticism and realism, and that conflict is at the heart of Little Children. Suburban tragicomedies have become their own subgenre, and director Todd Field acknowledges recent films like American Beauty and Happiness in sly ways. But Little Children is a far tricker work its predecessors, blurring the line between bucolic humanism and ironic detachment. The result is perhaps the most challenging film of 2006: it's flawed yet indelible.

Sarah Pierce (Kate Winslet) is a liberal-minded bookworm who dropped out of grad school to marry Richard (Gregg Edelman), an older, successful businessman who is also (as Sarah discovers) a porn aficionado and a bit of a pantysniffer. Sarah is befuddled by her upper-middle-class existence and ambivalent about her relationship with her daughter Lucy (Sadie Goldstein), who is as sweet and needy as toddlers tend to be. Sarah spends her days at the playground with Lucy, trying to ignore the banal chatter of fellow moms; the mononoty is broken one day by the arrival of Brad Adamson (Patrick Wilson), a stay-at-home dad known to the moms as the "Prom King." Sarah strikes up a conversation with Brad in order to shock her peers, but what begins as a joke quickly turns serious as Sarah and Brad find themselves urgently attracted to each other. Before long, they're engaging in sessions of enthusiastic sex while the kids nap. Brad's wife Kathy (Jennifer Connelly), a documentary filmmaker increasingly frustrated by her husband's repeated failures at the bar exam, begins to suspect that something is afoot. It's a familiar premise, but Field and co-writer Tom Perrotta (adapting his book) approach it with understated insight. While it'd be easy to judge Sarah and Brad for their infidelity and questionable parenting, Field also gives Winslet and Wilson the room to create a palpable, almost spiritual connection. The sex scenes are sweaty and vital, and they bring the film's understated visual strategy (lonely houses, treetops against a gray sky) and dry observation of playground routines (narrated in brilliant deadpan by Frontline's Will Lyman) into focus. We exist outside of the narrative until Brad and Sarah's affair allows us in, and even then our ability to engage in the story is determined by our capacity for empathy.

It's a complex challenge that Field presents, and Little Children complicates matters further by juxtaposing Brad and Sarah's story with the arrival of Ronnie McGorvey (Jackie Earl Haley), a "sex pervert" who has just been returned from prison to live with his long-suffering mother, May (Phyllis Somerville, great in a brief role). From the scene where Ronnie decides to take a dip and promptly clears out the town pool, Field masterfully plays upon our conflicted sympathies - Ronnie is capable of horrible things, but he's no less recognizably human than Larry (Noah Emmerich), an ex-cop who harasses the McGorveys out of an inflated sense of self-righteousness (not to mention guilt over his own sins). All of this could have played as a painfully simplistic work of moral equivalency, but again, Field gives us room to measure the divide between the characters' intentions and their actions on our own terms. Haley does excellent work here; living in a Rockwellian nightmare of ticking clocks and passive, smirking Hummels, Ronnie is a man slowly unravelling and threatening to break at any moment. When he finally does, it seems that Field is asking (in no uncertain terms) what parts of ourselves we must discard in order to put away childish things.

I realize that I've made Little Children sound more like a Sociology 101 midterm than a fun night out. Indeed, it is a difficult film to embrace, and its ambitions make its flaws (Mary B. McCann's stilted, obvious performance as the leader of the soccer moms, for instance) more glaring. At the same time, it's refreshing to see a film that places an enormous amount of faith in the audience's intelligence. Perrotta's screenplay is sharply funny, and Field demonstrates a flair for satire unseen in his good but delibrately somber first feature, In the Bedroom. Wilson does hilarious work as a "primary caregiver" pretty enough to dismiss the importance of beauty and goofily enamored with contact sports and skaters. Connelly's icy presence is perfect for Kathy. And Winslet is the heart of the film, giving another in a series bold, uncompromising and insightful performance; when Sarah begins to cry outside Brad's house, you can see the tragicomic soul of Little Children on her trembling face, which reveals both the child she was (and still is) and the grownup she might someday become.