Conceived as a low-cost showcase for developing new work, the new Sandbox series at SF Playhouse is a sort of midway point between staged readings and full-blown productions. It's an ideal venue to bring out local playwright Geetha Reddy's 90-minute one-act, for which this stripped-down production seems less like a deficit than a means of greater immediacy and thematic resonance. Feeling drenched by the flood of recent historical high-water marks — Oklahoma City, Y2K, Columbine, and 9/11 — one reluctant stay-at-home mom (Amy Resnick) holes up, hides out, and starts taking her kids' safety just a wee bit too seriously. It becomes clear through Reddy's sweeping but adroitly nonlinear narrative arc just how mom's increasingly frenzied survivalism has left her daughter (Marissa Keltie) and developmentally disabled son (Cole Alexander Smith) all the more absurdly estranged from their timid investment-banker dad (Brian Herndon), let alone the rest of the world. This big-hearted black comedy could come off as lame so easily, but Reddy sets a graceful example of restraint that is taken up by Nancy Carlin's unobtrusive direction and by the actors — particularly the shrewd, perceptive, irresistible Resnick.