A brilliant idea for a documentary, beautifully executed: Director-writer-editor-etc. Rob Whitehair follows some 250 kids, wee to teen, in five cities across the U.S. and Canada as they audition for and star in stage productions spearheaded by the Missoula Children's Theatre, whose patient, boisterous, and demanding directors transform a one-off into a life-altering experience. No surprise that the L.A. kids, staging The Little Mermaid, are the camera-savvy pros with impressive chops. And the ones from faraway Rankin Inlet, Nunavut, Canada, for whom live theater's a rare and magical thing, are the most shy and slightly stunned. But for most, if not all, of the subjects, the opportunities afforded by the MCT are extraordinarythe chance to find themselves by being someone else, with friends and rivals and siblings for whom plays are no longer playtime by film's end. Most of the kids interviewed talk about how they were troubled or in trouble before they got involved in theater. (Some still area few of the kids get the boot when they can't play well with others.) Good for kids just beginning to express themselves; even better for their parents. Hey, where's Guffman when you really need him?