Blondeau is not the first mini-model to stir up the sexualization debate. In 2007, a 13-year-old Dakota Fanning posed in a controversial campaign for Marc Jacobs.
Now, Elle Fanning, 13, has followed in her sister's footsteps as the face of Jacobs' fall 2011 campaign, while her fellow young costar, actress Hailee Steinfeld, 14, is the face of the Miu Miu fashion line.
Some say the grown-up beauty portrayed by the likes of Elle, Hailee and Thylane is giving other young girls unhealthy ideas about how they should look.
"We don't want kids to grow up too fast," said Shari Miles-Cohen, senior director of women's programs for the American Psychological Association. "We want them to be able to develop physically, emotionally, psychologically and socially at appropriate rates for their age."
And the debate is not likely to end soon.
The sexualization controversy extends to pint-sized pageant queens and prospective pop stars, too. A YouTube video of 8- and 9-year-olds dancing to Beyonce's "Single Ladies" spurred a similar uproar last year.
"People have always admired young ballerinas in scanty costumes, but those performances weren't explicitly sexual," Vivian Friedman, child psychologist and professor at the University of Alabama at Birmingham, told ABC News at the time. "There was an aesthetic that didn't remind you of being in bed."
Photos of Thylane, some in pink tutus and others in bed, illustrate the disparity.
French Vogue provocatively poked at this principle, running photos of Blondeau and two other tweens playing designer dress-up captioned with, "Quel maquillage à quel âge?" -- What makeup at what age?
"This isn't edgy," Feminsting.com editor Chloe Angyal wrote. "It's inappropriate, and creepy, and I never want to see a nine-year-old girl in high-heeled leopard print bedroom slippers ever again."
Sexualized images can have lasting effects on the young girls who see them.
An American Psychological Association task force found that sexualization by the media affects how girls think about femininity and sexuality, promoting "appearance and physical attractiveness" as key values. It's also linked to low self-esteem, eating disorders and depression.
"The research clearly shows that the fashion industry affects girls and women's images of themselves and their self-esteem if they do not meet the industry 'image' that is currently in vogue," said Paul Miller, associate professor of psychology at Arizona State University in Phoenix. "Even the very young are quite conscious of media images of what is 'pretty' and desirable."
In a photo not affiliated with Vogue, Blondeau poses topless on a bed with a young male playmate propositioning a pillow fight. And in another, she wears hip-slung jeans and no top with beaded necklaces covering her would-be breasts.
Many in the industry have defended the work as art. Others say it crosses a line.
"Any creepy child pornographer could plead 'artistic license,'" said Miller.
Thylane Loubry Blondeau's grown-up look is creating a stir.