At the lavish New York gala celebration of her 22nd birthday that opens Uptown Girls, Molly Gunn (Brittany Murphy), the rich, pampered, doodle-brained daughter of a legendary dead rock star, turns to her best friend and chirps, ''Am I turning into a hideous hag?'' The tough-love answer ought to be, Not yet, sister, but this tweeting has got to stop: Murphy's increasingly high-strung, self-conscious performances composed of squeaking, weeping, giggling, and purring to the camera threaten to become a caricature of the striking work she did in ''8 Mile'' and ''Girl, Interrupted.''
Then again, the retro-ditsy role of Molly -- who learns about adulthood from an emotionally wizened 8-year-old girl -- is enough to depress even the least flibbertigibbety of actresses. When her money runs out, Molly takes a job as nanny to freakily serious, hypochondriac Ray (Dakota Fanning), a prissy Miss Bossy ignored by her own self-involved, high-powered mama (Heather Locklear). Ray, dressed like a suburban matron, teaches Molly how to be responsible. Molly, stumbling as cliché demands in wobbly high heels, teaches Ray how to have fun. Unlike in ''Freaky Friday,'' no magic spells are involved.
Nor is there any of ''Freaky'''s marvelous charm in this ungainly Manhattan fairy tale, directed by indulgent sentimentalist Boaz Yakin (''Remember the Titans'') and inspired, claims producer Allison Jacobs, by haute-New York movies like ''Breakfast at Tiffany'''s. Fanning is wonderfully somber and owlish as a tragicomic specimen of precocity, but like every other character in the movie's baubly universe, in the end she's just an accessory to Molly's wardrobe of attitudinal poses.