PRETTY BABY - K-B Cerberus, K-B Janus.

"Exploitive" is the word that has been used about "Pretty Baby," because it stars a 12-year-old model in a story about a 12-year-old prostitute. But it takes a robust and humorous approach to life in a brothel, where the work done is less important than the community spirit; and "naughty" would be a far better word to describe the sex scenes, while the rest is decidedly nice.

The 1917 brothel in New Orleans' Storyville in which Louis Malle and Polly Platt have set their film is a cheerfully overstuffed residence populated by cherrfully overstuffed women and their children. That a daughter of the house should go into the communal family business is natural, and the fussing and excitement surrounding her debut seem not much different from those associated with more respectable ceremonies to launch young girls. Tea dances, packing to go off to college, weddings - those, too combine titillation with finery and giggles.

A hint of moral perspective is provided by those close to the activity but not part of it. The classic such role is, of course, that of the piano player, and Antonio Fargas' narrow-eyed view, as he presides over the Jelly Roll Morton accompaniment, delicately brings in the cynicism. Respectability, a concept treated like the prize for the best job done, sheds its transforming light ironically when Susan Sarandon as the young prostitute's mother, having "overcome her past" and been rewarded by being draped in fox pelts, makes her protegee over into a child again, complete with plaid hair-ribbon.

Neither of them provides any strong judgment, just a suggestion that there are ways of looking at brothel life unsuspected by the inmates. The true tone of the film is set by the character of E.J. Bellocq, played by keith Carradine, a photographer who is close to but not part of that world, a sort of Toulouse-Lautrec of the lens.

And like that artist, he is able to appreciate the visual vitality of the place while holding himself aloof from its consequences. The world he sees is, above all, picturesque - he could as easily be depicting washerwomen, giving equal weight to their grace and their weariness, but not taking up the question of their wages.

It's a subtlety of the picture that this ambiguity is maintained even though the photographer does step into the action. Because Carradine's Bellocq is young and childish, his love for a 12-year-old is charming, rather than perverse.

And what of that child? Brooke Shields, at 12, is a beautiful actress; that is, her beauty is inextricably mixed with her acting. She is able to play a child in the world of grownups in such a way as to remind us that children cannot be blamed for accepting whatever world they are given.