At 12, Pov knows the sexual geography of the riverfront area in Phnom Penh like the seasoned prostitute he has become. 'They like girls,' he said, gesturing to four middle-aged Frenchmen. 'Small girls.' He also knows a sun-blackened and tattered woman a few metres away. She will rent her daughter for the price of a hamburger. As the sun sinks over the Mekong, Sisowath Quay in Cambodia's choking capital is a slow-moving river of human traffic. Young couples walk arm in arm, tourists gaze at one of Asia's most beautiful sunsets and children like Pov ply their trade, zeroing in on what they call rich, foreign 'lady-boys', or gay men. In the crowd of mainly brown-skinned people, white men stand out like flies on a cake. Some are alone, wearing hats and jackets in the stifling evening heat, strolling or sitting on the river wall, eyeing the crowd. A man with a Liverpool accent calls Cambodia a 'sweet shop' before becoming suspicious and hurrying away. These are no idle boasts in a city where 12-year-old girls are hawked for US$20 to US$40, but the ages are often much lower. Campaigners against prostitution in Cambodia say children as young as three are still being trafficked and rented out all over the country, mostly to Asian men but increasingly to foreign tourists pouring in through some of the most open borders in the world. 'I know of a brothel with 100 underaged girls run by high-ranking police and military officials,' said Don Brewster, an American Christian who moved to Phnom Penh with his wife in 2004 to set up a shelter for sexually abused children. 'There are brothels in some parts of the country where the clients are brought in buses.' After a decade during which Cambodia earned its unwanted reputation as a haven for paedophiles, anti-trafficking campaigners have recently begun to bare their teeth. Dozens of foreign men have been imprisoned or sent back to courts in Europe and the US, many by the tough deputy head of Phnom Penh's anti-trafficking bureau, Keo Thea. The 2002 deportation to Vietnam of faded glam-rock star Gary Glitter, who was renting a house in the city centre, also served notice, said the then minister of women's affairs Mu Sochua, that Cambodia was no longer open for business to the world's child abusers. Last year, the local courts convicted two of Cambodia's most notorious paedophiles, Karl Heinz Henning and Thomas Baron von Engelhardt, of raping girls aged 10 to 14. Henning and Engelhardt, a ponytailed German who claimed aristocratic descent, paid US$30 per girl to pimps, often parents, before taking the children to a Phnom Penh apartment, drugging them with Ecstasy and videotaping hundreds of hours of sex sessions. Some of the children were bound and gagged while the men tortured them in Nazi regalia. The police were called after neighbours heard screaming. But these successes only scratched the surface. Mu Sochua quit soon after Glitter was kicked out of the country, saying corruption was making her job impossible. Two years ago, the US threatened sanctions after the State Department said Cambodia had failed to meet 'minimum standards' to tackle the trafficking of children. Today, with tourism increasing by 30 per cent a year and many police, judges and politicians taking bribes, the illegal sex trade is booming. US charity World Vision last year said that 15 per cent of the Cambodian boys they surveyed had been sexually abused before reaching their 10th birthday. About a third of the roughly 80,000 to 100,000 prostitutes in Cambodia are children, according to Canada-based NGO Future Group. The abuse of children is so routine that local newspapers barely cover it. 'It's levels of depravity,' said Irishman Kevin Doyle, editor of The Cambodia Daily. 'You think you've seen it all and then something new comes along.' Arrests are often taken care of with cash. Men pay off the families of the victims and the authorities in a country with a barely functioning legal system where the average civil servant earns about US$30 a month. 'The families are happy to get the money and drop charges,' said Sourm Dear, Cambodian director of Rapha House, a centre for victims of sexual abuse, who says his organisation has to pay the police to find missing girls. Traffickers and pimps, protected by military police and politicians, target poor, broken families, paying US$20 to locals for information on potential victims. Sarom Vath was 15 and living with her grandmother near the Thai border when she was approached by a woman with an offer to work as a waitress. Instead, the woman sold her virginity and locked her in a room with the buyer, a middle-aged taxi driver. 'It hurt a lot,' the victim recalled. She was sold to a brothel, drugged and forced to have sex with up to a dozen men a day. 'We were given pills and something to smoke, so I couldn't sleep and didn't care about anything.' Now 16, and living in a centre for abused children, she is angry and rebellious, but says talking about what happened helps 'lighten my heart'. Children like her get a brutal crash course in the economics of flesh. For many - 38 per cent, according to a 2007 report by the International Organisation for Migration - entry into the sex trade comes by selling their virginity, sometimes for as little as US$100. Some do so 'voluntarily'; most are trafficked or tricked. Rady Yen, for example, was 15 and alone on Sisowath Quay when she agreed to work cleaning tables, only to find that her virginity had been auctioned off to a Japanese tourist. 'I got sick and couldn't see any more men,' she said. She escaped, but the market value of girls who stay in the sex trade plummets: a couple of hundred dollars for a pre-teen, up to US$40 for a 12-year-old and on a steadily sliding scale thereafter. Sarom Vath has no idea how much she changed hands for, but thinks it was US$5 to US$6 a time. Crushing poverty fuels the trade. In a festering Phnom Penh slum known simply as 'the building', naked children play on garbage dumps, watching their parents hawk their 13-year-old daughter to middle-aged tourists. She is the only thing of value they have. The country's poverty stems from the US bombing much of the country relentlessly for three years in the early 1970s, laying the foundation for the rise of the Khmer Rouge regime, which ran Cambodia into the ground and may have been responsible for more than a million deaths. 'Cambodians have developed a numbness to horror because of their history,' Mr Brewster said. 'There are no barriers; they will do anything for money and they live for today.' Astonishingly, given how freely paedophiles operate there, Sisowath Quay is the most heavily watched area of the country. Undercover police and NGOs patrol the area and the post-2002 crackdown has pushed some of the trade underground. The notorious brothel area of Svay Pak, on the outskirts of Phnom Penh, no longer sells children openly on the street to men with British, American and Irish accents, although pimps with mobile phones still hover around the area. But outside the capital, anything goes. In Poipet, a booming town on the Thai border fuelled mostly by gambling and prostitution, tuk-tuk motorcycle taxis ferry hundreds of Thai, Chinese, Japanese and other tourists daily to brothels on the Cambodian side, where children of any age can be bought with a handful of dollars or Thai baht. Street vendors even sell Viagra for about US$14 a pack. On Sisowath Quay, in front of the city's best restaurants, Pov and his friends eat a pizza bought by a tourist. Like many of the street children here, he is an unsettling mix of naivety and knowingness, his hand resting on my thigh as he pleads for the name of my hotel. He and his friends are desperate because he knows that most of the foreign men come for girls. When a photographer begins to take pictures, the boys drop their sales pitch, curl up like cats on the Quay wall, and smile shyly like children.