Kids are natural hecklers--they can't imagine they're not part of the action onstage, so they speak up, talk back, and otherwise break the fourth wall. The likable Jerk Alert Productions folks harness this natural exuberance by making the audience an integral part of their improvised children's show. The kids supply the characters' names, their favorite foods, the scary things they'll encounter during their adventures--and every step of the way they say how they like the story, what they think will happen next, and whether the costumes are right. It's a format parents have used at bedtime at least since the invention of children's books, and it works here too, helped along by the improvisers' friendliness and looseness and by the relaxed we're-here-to-have-fun atmosphere they create despite the cavernous space. Through 4/30: Sat 1 PM. Lakeshore Theater, 3175 N. Broadway, 773-472-3492. $8.