Every few decades, we get a superior demon-child thriller (see: The Bad Seed, The Omen). In part they work because they cast unknown child actors instead of preteen stars looking for that change-of-pace role to ease them out of the G-rated ghetto (avoid: Macaulay Culkin in The Good Son). Here the implacably menacing 9-year-old (Jacob Kogan) is a well-coiffed piano prodigy obsessed with mummies and Set, the Egyptian god of chaos. No wonder his Fifth Avenue parents (Sam Rockwell and Vera Farmiga) soon have cause to regret his private-school tuition. He's a savant in psychological warfare, prompted—of course—by the arrival of an infant sister who disturbs the family balance. The baby's incessant crying, the mother's nervous collapse, the father's bewildered reaction, the boy mysteriously popping up behind them at night—Joshua makes parenthood itself into a horror movie. And just across the park, in view of the family apartment, stands the Dakota, making little Joshua close cousin to Rosemary's baby.