Why do people even have children?'' screams a kid-tormented rent-a-cop (played by poor, slumming Steve Carell). Sleepover, Hollywood's latest slimy incursion into very early adolescence, leaves the question tantalizingly unanswered. Our heroine Julie (''Spy Kids''' Latina Alexa Vega, carefully shorn of ethnicity) and her nail-polish-deep friends say stupid, improbable things like ''For the love of carbs!'' and do stupid, improbable things like enter a competitive scavenger hunt against the witchy ''Pleathers,'' whom they resemble in every aspect save their noble tolerance for the token fat girl. But at heart (and I use the term figuratively), they're all Brownie terroristas, brand-dropping their way from B&E to light fetish (shoe-sniffing and voyeurism -- not just for boys anymore!) to an Internet rendezvous with a lonely male teacher. How adorably illegal! Yes, it's all a harmless lark. Which is why the only thing that could redeem this sour patch of candy-coated crud would be a final shot of Earth exploding.