I walked away at top speed, but I've not been able to shake the memory or the knowledge that this boy had at some stage been recruited by an adult into a terrible world of exploitation.
In a country with some of the world's most breathtaking sites and the most hospitable people lies a sick undercurrent of child rape and abuse.
The scariest part is how easy it is to find.
Westerners travelling through Cambodia are often offered sex. Picture: Gavin Fernando, news.com.au
A PLAYGROUND FOR CHILD ABUSERS
Cambodia has been described as a paedophile's heaven.
The country attracts more than five million tourists per year, drawn to the picturesque Angkor region of Siem Reap, the beaches of Sihanoukville, and the Khmer Rouge Killing Fields.
But child trafficking remains a nationwide problem, fuelled by locals and westerners alike.
Just last week, British doctor Clive Cressy, 69, was arrested at a cafe in Phnom Penh on suspicion of abusing four underage girls aged between 12 and 15.
Local police allegedly found a suitcase containing Barbie dolls, sex toys, coloured pencils and children's clothing while raiding his apartment.
They claimed he paid up to $A4000 (NZ$4300) to have sex with an underage virgin; a big industry "selling point".
Australians have likewise been linked to numerous cases over the past few years.
Last year, notorious South Australian paedophile Anthony Munro - who news.com.au revealed to be a person of interest in the 50-year-old mystery of the missing Beaumont children - was under investigation by Cambodian police for allegedly abusing at least two underage boys.
According to UNICEF, about a third of Cambodia's 100,000 sex workers are children - and they're disturbingly accessible.
As a single male walking through the tourist district, shady tuktuk drivers would whisper "Special massage? Fresh young girl?" as I walked past them.
I heard shocking stories from western travellers who accepted drivers' offers for "lady boom boom", only to be confronted by prepubescent girls in private run-down buildings on the outskirts of town.
Cambodia has a huge child trafficking problem. Photo / Gavin Fernando, news.com.au
UNICEF Cambodia spokeswoman Iman Morooka told news.com.au many children are deliberately removed from their families and placed in institutions where child rape is prevalent.
"Commercial sex exploitation of children happens mostly in entertainment establishments," Morooka said.
She said karaoke bars and massage parlours are the main venues. Here, scantily-clad girls of all ages line up in a row, and customers choose who they want.
In some cases, children are trafficked from neighbouring countries like Vietnam. In others, they're sold off by their parents to recruiters, who target poor and rural families claiming they can offer their kids an education and a better life.
Morooka said a culture of silence often accompanies this, which enables the industry's continuation.
"One barrier to protecting children is when families and communities do not speak out, even when they are aware of what's happening in their community, because they think it is not their business to ask questions," she said. "This silence provides cover to people who abuse, exploit and rape children."
Local orphanages - a common tourist attraction - have also come under fire.
Human rights organisations say so-called "orphanage tourism" provides easy access to children, who may be encouraged to say and do anything for cash.
In 2015, former NSW Young Australian of the Year Tara Winkler warned the permittance of physical interactions in such institutions was an open invitation to sex tourists.
"Even though the majority of people who want to visit centres are good people who only want to help, if they are allowed in to provide love and affection, then the same access is provided to potential predators and sex tourists," she told Fairfax.
In 2013, the Australian-run orphanage Love In Action was shut down by Cambodian authorities, after it was suspected of beating and trafficking its children.
EFFORTS TO CRACK DOWN ON CHILD TRAFFICKING
Donald Brewster and his wife Bridget have spent over a decade fighting human trafficking in Cambodia.
In 2005, they sold their home in the US, quit their jobs, moved to Cambodia and founded Agape International Missions (AIM) - an organisation devoted to rescuing victims from within the industry.
"(Trafficking venues) are all over the country," he said. "There isn't a government in the world which cannot do more.
"It's a question of priorities, especially when it comes to women and children."
On the plus side, there are many success stories. Since AIM's launch, Brewster says the programs have helped more than 3000 girls and women escape the industry.
He referred me to the story of Sokha Chan, a girl who was sold in a virgin sale to an American ex-Marine when she was just 7.
Recruiters target poor and rural families claiming they can offer their kids an education and a better life. Photo / Gavin Fernando, news.com.au
For five years, Chan was transferred between different illegal brothels, locked in a dark room and abused for cash.
Five years later, at the age of 12, the Brewsters helped to free her. Police raided the venue, and the girl was brought to AIM's after-care centre, given new clothes and a princess crown, and granted freedom for the first time.
She eventually obtained a US visa, and now - 10 years later - works as a nail technician and a baker.
"I want to share my story because I want the people who helped me to know they made a difference," Chan told ABC Nightline in the US. "They didn't even see my face or know my name when I needed them the most, but they still helped me! I want to inspire people to help other girls."
Even Hollywood celebrities are speaking out.
In February this year, Ashton Kutcher gave an emotional speech before the Senate Foreign Relations Committee, urging the US to do more to combat the problem.
"I've seen video content of a child that is the same age as mine, being raped by an American man that was a sex tourist in Cambodia," he said.
"And this child was so conditioned by her environment that she thought she was engaging in play."
Kutcher co-founded an organisation that uses software to fight human trafficking, which has identified over 6000 victims of modern slavery.
As for tourists, UNICEF's advice is simple: don't visit orphanages, don't treat children as tourist attractions, and if you see any potential cases of child exploitation, alert the authorities.
