Little Children By Tom Perrotta

Unhappily married Sarah passes her days at the local playground with her three-year-old daughter. When happily unemployed Todd (also married) and Sarah meet, their attraction is immediate. They begin a passionate affair just as their suburban utopia is rattled by the arrival of registered sex offender Ronald James McGorvey. With McGorvey in town, disgusted parents wonder if any of their little children will be safe.