It's a "Cinderella story". A "fairy tale". But is it?

"It's not a fairy tale; it's a cliche," said Ms Sara Ziff, founder of the Model Alliance, discussing fashion's favourite new narrative, that of a 14-year-old Israeli who went to Paris in search of a modelling career, met designer Raf Simons in a Dior store and ended up opening the Dior couture show this month.

"It's once again using girls to sell clothes to women."

A season after the more mature were widely celebrated in advertising campaigns such as Celine's (Joan Didion) and Saint Laurent's (Joni Mitchell), complete with numerous articles positing fashion's embrace of the silver dollar, the fashion pendulum has, it seems, swung dramatically in the opposite direction.

Aside from Dior's new find, Sofia Mechetner, Chanel has announced that the face of its eyewear campaign will be Lily-Rose Depp, 16, daughter of Johnny Depp and Vanessa Paradis. And Kaia Gerber, Cindy Crawford's daughter, has landed a photo spread in the September issue of CR Fashion Book, Carine Roitfeld's magazine. In one picture, she's wearing thigh-high leather Versace platform boots; in another, cat-eye make-up, a Prada dress and a pout. She's 13.

We're back in the days of Brooke Shields declaring, at age 15 (and in the 1980s): "You want to know what comes between me and my Calvins? Nothing", and the 1990s world of photographer Corinne Day, a teenage Kate Moss and the waif. Almost two decades later, isn't it time we moved on?

If the increasingly vociferous demands for diversity on the runway should have taught us anything, it is that consumers increasingly want to see models who look like them - all kinds of them. And most consumers of adult fashion are, shocking as it may seem, actual adults.

To be fair, there has been some movement between then and now. There is unquestionably heightened awareness within the industry, not to mention within the law, when it comes to the need to protect underage girls working in a grown-up world.

(Still, it is revealing that models are almost always referred to as "girls" by the industry itself; they aren't called "women".) Three years ago, all 21 international Vogues signed and published a pact pledging that they would not use models under 16 (though this has occasionally been circumvented, as in the case of Gerber, who recently appeared in Italian Vogue, the photos used as part of an "age issue").

In 2007, both the Council of Fashion Designers of America (CFDA) and the British Fashion Council issued health guidelines that strongly recommended (in the case of the US group) and required (the British council) that designers use models who were at least 16 for runway shows.

In 2013, after lobbying from the CFDA and the Model Alliance, the New York state legislature passed a law stating that all models under 18 must be treated as child performers, with all the related regulations, from limited work hours to trust accounts, supervision and checkups (and that brands must have a permit from the state Department of Labor, as must the models).

Meanwhile, Mr Ivan Bart, president of IMG models, the agency that represents Gerber, said it does not allow models under the age of 16 to do runway work. And according to a spokesman for Dior, its 14-year-old, Mechetner, was chaperoned at all times and has returned to Israel for school, her future relationship with the brand to be determined.

Even more, there is increasingly a narrative around models themselves, an effort to move them from nameless mannequins to personalities.

Mechetner is being "sold", as Ms Michelle Tan, editor of Seventeen, put it in a phone call, as "a role model for the boldness of teens". The Gerber story is one, as Ms Tan tells it, of "Hollywood royalty: the next generation", while Lily-Rose Depp's fable is about "Uncle Karl introducing her to fashion". Uncle Karl being Karl Lagerfeld, who once upon a time, employed Depp's mother as a muse.

And yet, no matter how many parental chaperones and stories are invoked, and no matter that these very young girls are the extreme rather than the rule, this doesn't solve the public perception problem that, as Ms Ziff says, "when you dress children up in make-up and high heels, the implication is that they are sexual objects and more often than not, that is how the images are read by the public".

Fashion is in essence an industry based on deception: the promise that if you simply wear this, you will look better/cooler/thinner/ taller/ more powerful than you really are. The suit was created, after all, to craft an illusion of physical perfection. That's the upside. We all benefit.

But the pretence that these girls are older/more knowing/more seductive than they can possibly be at their age - and that anyone who buys the clothes they are modelling may look like them, when they clearly can't because they are not in their early teens, a distorted physical time when girls have the bodies of children, but the height of an adult - is the downside.

Unlike their silver counterparts, who are celebrated precisely because they are the age they are and hence held up as inspiration, these kids are celebrated because they don't look anything like the age they really are.

No matter how much you take care of them, this disjunction between reality and image is jarring. It's telling that models themselves, including the most successful ones, have publicly addressed this.

Young models are put in a situation "that treats them as adults and they do not know how to work with that", Canadian model Coco Rocha, 26, told journalist Anderson Cooper in 2011. "They are just thinking, 'How do I please you?'"

She added that she believed 15 was "too young" for the business.

Of her own career, Kate Moss, 41, told Vanity Fair in 2012: "I see a 16-year-old now and to ask her to take her clothes off would feel really weird. But they were like, 'If you don't do it, then we're not going to book you again.'

"So I'd lock myself in the toilet and cry and then come out and do it. I never felt very comfortable about it."

So what is the allure? The imperative of the new, presumably, though you can be new at 21. Pressure, perhaps from the girls themselves.

"Teenagers are ambitious these days," Ms Tan said. "You can't fault Sofia for that, though I maybe wish she had waited a bit. It's a reflection of the moment."

Fashion loves to reflect a moment. It also loves transgression; though given that youth-in- women's-clothing is now a pretty familiar story, it's not really so transgressive.

Maybe it's finally time it has a new happy ending.

NEW YORK TIMES