Is there a bigger demographic than parents? Like the undead in a zombie apocalypse, there are more of them every day, every hour, every minute, every second. Normal people become parents just like that. If you've become one of them or know anyone who is, you're part of the ever-expanding niche audience of Rated P... for Parenthood, Actors' Playhouse's annual summer musical soufflé. It's written by Sandy Rustin, an actress and mom cool enough to star in shows her kids shouldn't be allowed to watch (like HBO's Boardwalk Empire or Neil LaBute's Broadway show Fat Pig), and comprises songs and sketches charting parental joys and roadblocks from conception to college. The musical direction ranges from hip-hop to a Texas two-step, and the topics span late-night feedings, PTA meetings, and sex-life maintenance for a decidedly adult audience; Rustin employs the word vagina like Quentin Tarantino abuses a certain racial slur. Julie Kleiner, Jim Ballard, Henry Gainza, and Amy Miller Brennan round out the topnotch cast, under David Arisco's direction.