Having 'The First Lady of the Theatre' as a mom looks like nothing but gravy at first glance. And Jamie MacArthur, 19-year-old son of famed actress Helen Hayes wouldn't try to deny how helpful it can be to have an inside track to show business. But he'd remind you of this: VIPs can always give you a push in the right directon, but once the cameras start rolling you're on your own. And that's exactly where he is at the moment. RKO's The Young Stranger will give you an idea of what the blue-eyed, 160-pounder can do.