Rachel Kirby, from north London, was signed up by the Select Model Agency last month after she was spotted shopping with a friend. By her 13th birthday she was expected to be earning pounds 500 a day.
But the decision to employ Rachel has prompted concern over the increasingly young age that models begin their careers, and the example they set for women and young girls, many of whom are obsessed by their weight. A recent survey revealed that half of 11- and 12-year-old girls believed they were overweight.
The Select agency, which has 70 schoolgirls on its books, denied yesterday it was exploiting Rachel. It said that with the backing of her parents, James Kirby, a chartered engineer studying law, and his wife Gaye, a charity worker, it had put her career on hold to protect her from "press interest".
Although Rachel is only 12, she is 5ft 10in, and appears much older in photographs taken for ID magazine. She is heavily made-up and pouting in the style of adult models, but she has the skinniness of a child known as the waif look.
Dr Dee Dawson, who runs the Rhodes Farm Clinic in London for anorexic children, said: "There are two problems here, one for the girl who will be absolutely terrified by the changes happening to her body, because she will no longer be placed in the 'superwaif' category.
"Secondly there is the problem for the 16- and 17-year-old girls who see these pictures in magazines, and will aspire to a figure which is completely impossible."
Other agencies said yesterday they would resist employing such young girls in the first place. Although most will take on 14-year-olds part- time, they would be reluctant to expose them to the spotlight until they were at least 16.
Jose Fonseca, director of Models One which represents Yasmin Le Bon, Twiggy and Jerry Hall, said: "You are playing around with their childhood, it's just too young and they need their time to grow up and for their bodies to change shape."
She added: "The older models have actually become much more popular because women are fed up of buying clothes and make-up that is modelled by a 16- year-old. A lot of the American designers, including Donna Karan, are using the older ones because women want to see real women."