SVAY PAK, Cambodia, March 21, 2010 -- Clay Butler, a 27-year-old evangelical Christian from California, points to a group of children playing in the street and said, "I know kids in that group who are being trafficked. I know the situations, I know the brothels that they're in."
Butler runs a community center in the village of Svay Pak, the epicenter of Cambodia's raging child sex trafficking epidemic. It's a place where, on any given night, many of the children will be sold -- by their own parents -- for sex with strangers.
He is one of many American Christians who have come to this impoverished, war-ravaged country to protect some of the world's most vulnerable children.
"I think the most exciting part of Christianity is living it out," Butler said. "This stuff is not fun at all, but there is a deep fulfillment in laying your life down for somebody else."
Other Americans Christians are practicing an even more daring version of their faith. A group called the International Justice Mission regularly sends undercover agents into the brothels to gather video evidence. The group then works with local police to bust suspected sex tourists, oftentimes American men.
They also rescue child sex slaves like Bella, a 15-year-old who says she was forced by pimps to have sex every day.
Bella was sold into slavery by her mother. In Cambodia, it can be astonishingly easy to buy a child from the family. During a recent visit to Cambodia, ABC News was able to negotiate -- in broad daylight -- with the mother of a 15-year-old girl. The mother said she was willing to sell her daughter to a foreigner for marriage.
When asked how much it would cost, the mother answered, through a translator, "It's up to you."
In response to a question about whether her daughter had been with another man before, she said, "No, no, no. If you don't trust you can take her to the hospital… for a medical examination."
So why is it so easy to buy a child on the streets of Cambodia? Poverty is one explanation, but some Christians say the ghosts of history play a role.
Pastor Has Seen Cambodian Child Sold to Pay for Superficial Items
Cambodia endured a massive genocide in the 1970s, during which children were forced to spy on and even execute their parents -- and the educated and religious communities were nearly wiped out.
Pastor Don Brewster, who runs a shelter for former child sex slaves and works with Clay Butler, said he believes that Cambodia now suffers from a moral vacuum.
"These families will take a loan to buy a TV which they can never pay," Brewster said. "They can't feed themselves, never mind buy a TV, but they know, 'Hey, I've got my ace in the whole. I can sell my daughter.'"
Bella, the 15-year-old rescued by the International Justice Mission, is now staying at Pastor Brewster's shelter, where she said she is finally getting help.