Todd Field's Little Children's screenplay was written in collaboration with Tom Perrotta, on whose eponymous novel it's based. Perrotta wrote the funny, ironic screenplays for Election, Bad Haircut, and Joe College before this. But though mildly satirical at times in its vision of middle-class white infidelity, this second film (at last) from the director of 2000's powerful In the Bedroom, with its themes out of Cheever or Updike, also moves toward the solemn and the shocking.

One big reason for that is a second plot about a just-released sex offender and a troubled ex-cop who turns into a self-appointed protector of public morality campaigning to drive the ex-prisoner out of town.

Brad (Patrick Wilson) is a househusband caring for his little boy while feebly preparing for his previously failed bar exams. He has a gorgeous but emasculating wife, Kathy (Jennifer Connelly), who's a successful PBS-style documentary filmmaker. Sarah (Kate Winslet), with an MA in English, in charge of a recalcitrant little girl with whom she has little patience at times, has a well-off distant husband (Gregg Edelman) who's a pretentious adman who gets off on Web porn. Sarah and Brad meet in a park where moms take their kids, in East Wyndham, Massachusetts. They wind up kissing when they first meet, mainly to shock the other moms.

Brad and Sarah spend a lot of the summer minding their kids together at the municipal pool. This turns into a torrid affair with frequent sex at Sarah's husband's large house. They're attractive, and attracted, and their general dissatisfaction with their spouses and with where they are now heightens their need to throw themselves at each other with the utmost abandon.

Meanwhile Ronnie (former child actor Jackie Earle Haley, vividly remembered from Bad News Bears and Breaking Away and strong in a new way here) has come into town: he's the sex offender, a painfully self-aware one, and he lives with the one person who loves him, his aging mother Ruth (a convincing Phyllis Somerville), while the ex-cop, Larry (Noah Emmerich) wages his war as a one-man "committee." Larry and Brad have met and Larry persuades Brad, who already wastes time watching boys skateboarding when he's supposed to be boning up for the bar exam, to join a night touch football league team made up of cops – and thus the infidelity and the sex offender elements are linked. But they would be anyway, because this is a small community. And one particularly hot day Ronnie comes to the municipal swimming pool and causes an outcry when he's spotted ogling young girls under water.

The other moms from the park, who were afraid of Brad and called him "the Prom King," are gently satirized by a voice-over narration spoken by Will Lyman, of Frontline on PBS, which sounds like a high school educational film. Perrotta is, after all, a comic writer. But more of that later.

The movie has a bright, intense, clear visual style, sometimes making use of extreme close-ups. Since the acting and directing are fine, this gives things a feeling of authority. It's also effective in underlining both the satirical and the sensual aspects of the story, and heightens the emotional effect when the narrative lines move toward crisis.