The discovery of a magic wish-granting rock spreads havoc in suburbia, first among a gaggle of kids (Jimmy Bennett, Jake Short, Trevor Gagnon, Jolie Vanier), then among their even more childish parents (James Spader, Leslie Mann, Jon Cryer, William H. Macy). Writer-director Robert Rodriguez returns to Spy Kids territory, with even better results. His story is childlike without being puerile, his young actors have just the right level of breathless fervor and his grown-ups just the right tongue-in-cheek pomposity. The special effects are endearingly cheap, like an old Saturday-morning kids’ adventure; Rodriguez manages to spoof the genre while rekindling the nostalgic pleasure of gathering around the TV in pajamas with bowls of Froot Loops and Cocoa Puffs. It’s perfectly silly, but irresistible fun.