“The Bedwetter,” based on the comedian’s memoir, is an off-color character study with family-friendly morals, now running at Arena Stage. Composer David Yazbek contributed new material to this tightened and revised version of the show. Its narrow focus on Sarah’s perspective — nearly every song reflects her interior or how she’s perceived — paints a touching pint-size portrait. Under the direction of Anne Kauffman, who’s known for shepherding thoughtful dramas, the actors imbue the story with dimension and heart, and they’re reason enough to see this production.