Some time between their last Barbie doll and their first boyfriend, pre-teens have become a niche target for lingerie firms, vying to secure their favours as lifelong consumers of frilly underthings.
But creating bras for the barely-pubescent is a potential minefield for brands: a too-bold design or a bit of padding in the wrong place, and they can stand accused of turning their junior clients into sexualised little Lolitas.
At the International Lingerie Fair taking place in Paris this weekend, a dozen firms had models aimed at teens and pre-teens — also known as "Tweens" — including girls as young as nine.
"For girls that age, the main challenge for brands is to appeal to their mothers," said the fair's head Cecile Vivier. "You have to be reassuring, and not too sexy."
Most of the pre-teen lingerie on offer at the Paris fair played it safe with simple, lace-free little triangles, sometimes dubbed training bras or bralettes.
Petit Bateau, which specialises in cotton children's underwear, offers girls aged 12 to 16 triangles with a hint of padding — which it says is aimed to hide the nipple, not boost bust size.
For most girls that age, explained Petit Bateau's wholesale commercial director Muriel Mertz, a first bra aims chiefly to conceal the changing figure.
"It's all about comfort and invisibility — you mustn't be able to see the nipple," she said. "We are still in a kid's world, before girls turn to something more womanly, more seductive."
Skiny, an Austrian firm which designs underwear for "the whole family", also offers demure-cut, bright coloured, teen bras aimed at girls from 10 upwards.
"It is really carefully done — with no padding," said the brand's international sales manager Stefan Breitband. "We're not really about sexy lingerie. There's no attitude."
For Tween lingerie is risky territory: last summer the French brand Jours Apres Lunes caused a stir with a line aimed at four- to 12-year-olds that was attacked in Britain and the United States as sexualising little girls.
While its bra and panty sets, in black-and-white or pink, were innocent enough, the ad campaign offended by showing children mooning in their underwear, dolled up in womanly hairdos, shades and ropes of pearls.
The brand's founder, Sophie Morin, hit back arguing that her clothes aim precisely to bridge the gap between "plain cotton undies, and the lingerie world whose products are too sexy for children."
Girls are hitting puberty younger
A US research team last year found that nearly a third of clothes targeted at pre-teen American girls had "sexualising characteristics" — such as the use of slinky red or black materials or leopard-skin prints, or cuts that emphasised the buttocks or breast area.
American pre-teen store Abercrombie Kids has repeatedly been accused of overstepping the line — in 2002 for selling thong underwear with "wink wink" and "eye candy" printed on the front, and last year for a kid's push-up bra.
Concerns about the appropriateness of pre-teen lingerie has prompted Britain's retail consortium to publish guidelines for manufacturers targeting young girls, urging them to avoid lace and push-up bras.
"First bras should be constructed to provide comfort, modesty and support but not enhancement," says the text published last year.
To complicate matters further, the teen lingerie boom coincides with a trend towards earlier physical development of children which is seeing many girls hit puberty younger.
According to a US study published by the journal Pediatrics in 2010, 15 percent of American girls now have breasts by age seven, with similar trends observed in Europe and Australia.
Just what is causing the shift is not fully understood, with possible factors including obesity or hormone-disrupting chemicals in the environment — but whatever the root cause, the result is that many teens need real, womanly bras from a young age.
Lise Charmel's teen brand, Antigel has seen sales for deep cups, from D to G, soar by 46 percent in the past three years.
"Young girls with a large bust have to go into stores full of women's lingerie — all lace and frills — which just isn't right for them," said Sophie Grimaud, the brand's public relations director.
So what kind of bra is right for these teenagers?
"Girls that age want colour, graphic lines," said Grimaud. "They are not trying to show off their body."
That said, Antigel — which admittedly targets a slightly older age bracket, starting at 15 — veers well into sexy territory, with an offer that includes deep-plunging bras and suspender belts.
Likewise Cleo, an older teen brand specialised in large cup sizes, offers retro-looking cuts, polka dots and 50s prints on bras and boxers.
"We target fairly confident young girls, who want to have fun with their lingerie, and who don't want to feel like their mothers," said Marlene Castanheira, Cleo's sales director, when asked about the sexier looks in its catalogue.