This story begins in Sierra Leone, in West Africa, although it could be in any one of more than a dozen countries wracked by civil war. A young woman named Mariama, interviewed by the acclaimed documentary producer Sorious Samura, tells how she was abducted from school and used as a sex slave for years by a rebel group notorious for its cruelty.
Mariama tells how the rebel commander adopted her as his "sister", and then allowed his men to abuse her. "The guy who I was with did not do anything to me. But the others forced me when this guy wasn't around, saying that if I refused, they'd kill me. So they usually raped me. I had to accept it as I wanted to save my life, knowing that one day I would be away from there."
Mariama's voice is unusual, in that the outside world rarely hears first-hand the tales of horror faced by children in war zones. But unfortunately, stories such as Mariama's are all too common.
UNICEF, the United Nations Children's Fund, says millions of children each year are bought, sold or kidnapped into slavery. Another international aid group, Save the Children, says more than 120,000 girls and young women, some as young as eight years old, have been forced to take an active role in armed conflicts, many of them in Africa.
Pamela Shifman, UNICEF's adviser on violence and sexual exploitation, says girls are especially vulnerable in war zones. "In terms of trafficking, we see that trafficking flourishes during conflict because of a breakdown of law and order, because of porous borders, that it's easier to move children between countries.
"We see that children, especially girls, are targeted for sexual violence, including sexual exploitation," she continued. "We've seen rape used as a weapon of war in conflicts throughout the world, and we also see, very often in conflict situations, a dramatic rise in prostitution, and we see children, especially girls, suffering from that."
While some of the worst abuses take place in war zones, Ms. Shifman says the trade in children for sexual purposes knows no boundaries. She says child traffickers have many ways of capturing their prey. "Sometimes children are lured into the hands of traffickers through false advertising; sometimes children are lured into the hands of traffickers by promises of a better life; but very often children are lured into the hands of traffickers because they see no alternatives for themselves and their families, and they are desperate, and so they are willing to believe anything and do anything in order to survive."
While much of the trafficking in children takes place in Africa, rights activists say it is happening in almost every part of the globe.
Namik Shehaj, who runs a UNICEF-funded child protection project in Albania, says impoverished parents sometimes sell their children out of desperation. "Actually, the parents send the kids to Greece because they see it as a possibility to earn money. And this is a contagious disease, because you see your neighbor, he has sent his kid to Greece; he has gone there himself even. So you ask yourself, 'Why shouldn't I send mine?' The only reason these children are trafficked and exploited is the poor economic situation of the family."
Children's advocates say well-organized criminal gangs take advantage of poor families, offering them often-paltry sums of money for their children. In many, if not most cases, young girls end up in the sex trade.
Fifteen-year-old Yasmina, a girl rescued by Mr. Shehaj's organization, was originally sold to work as a street beggar. Later, she was forced into prostitution.
She tell her sad story. "I was four years old, too small. I was with a neighbor. He gave some money to my father and then took me there, to Greece. My father told him 'Take my daughter and keep her there'. My neighbor, who's called Todi, gave my father 25,000 leke ($253.00 U.S.), so it was like my father sold me."
Carol Bellamy, who spent the last 10 years as executive director of UNICEF, says there is no magic solution for ending child trafficking. The problem, she says, is that the business of buying and selling children, especially girls, is so profitable.
"In many cases this is very lucrative business, backed up in many cases by organized crime. If you can make money out of something, there will always be those who look for ways to get around the laws, and get around the pressures." Ms. Bellamy add that the solution is that "more pressure, more laws, more attention has to be brought to the issue of trafficking in people. But understand that we are up against very strong, very powerful enemies."
Because it is so lucrative, Ms. Bellamy says progress in the fight against child trafficking has been maddeningly slow during her decade at UNICEF. Selling children, she says, is beginning to rival the drug trade and the arms trade in profitability.
Hearing all the horror stories, and depressing statistics, Ms. Bellamy admits it is sometimes hard to be optimistic. But addressing a news conference on her final day as UNICEF director, she listed among her proudest achievements that UNICEF had played a pivotal role in shining the spotlight of international attention on the exploitation of children.
She said, "I can say with certainty that governments are no longer free to ignore these abuses as they were just 10 years ago."