Strangers can walk off the street into bedrooms, where up to 12 children sleep crammed together on stained mattresses.
The smiling children know the routine - they run to the visitors, calling out in unison: "Hello, welcome!"
But strangers should not come to this house tucked away in a Phnom Penh suburb, behind high iron gates, which is home to 65 children aged between five and 17.
International research shows that orphanages and residential care institutions take a toll on children's emotional and personal development because they are separated from their families.
This leaves them vulnerable to exploitation and abuse and seemingly endless broken relationships.
Much of their plight comes at the hands of mostly well-intentioned foreigners. Australians are among the largest donors and volunteers in Cambodia's booming orphanage industry.
A newly released survey of tourists in the Cambodian town of Siem Reap, near the Angkor Wat temple complex, found that 70 percent of potential volunteers at the country's orphanages believe that residential care is the best way for children from poor families to get access to an education.
According to Friends International, a non-government social enterprise organisation , 75 percent of potential volunteers were not aware that most children in residential centres in Cambodia are not orphans and 60 percent did not know orphanages were sometimes run as profit-making businesses.
Despite a five-year campaign by Friends International and other NGOs warning that children should be kept in their communities except in emergencies, the number of children living in 600 orphanages and residential care centres in Cambodia has grown to a record 47,900, according to a recent survey by the Cambodian government and the UN children's agency UNICEF.
Indeed, the number of orphanages across the country has doubled in the past five years, while the number of orphans has dramatically decreased.
There are now seven times more children in Cambodia's institutions than there were in the early 1980s, when the aftermath of the Khmer Rouge's murderous rule left an estimated 74,000 children without parents.
The government, under pressure from UN agencies and a consortium of more than 50 NGOs, is moving to implement a law requiring that children's residential centres be approved and registered, which is aimed at forcing many to close.
The government wants to reduce the number of children in orphanages by 30 percent in three years.
But Cambodia's supervising ministry of social affairs employs only 14 social workers in a country where corruption is endemic and unscrupulous orphanages have flourished for decades.
Social workers warn that many of the children have become money-making tourist attractions and sexual abuse is suspected of being rife in centres where there are few checks to identify western child abusers who travel to Cambodia to gain easy and unsupervised access to children in care.
The former director of an anti-pedophile NGO has been charged with sexually abusing 11 boys under his care in an orphanage he headed.
In the early afternoon, half a dozen children from Phnom Penh's Poor Street Children and Orphans Training Centre rehearse for a classical Khmer dance and monkey performance a few hours later ofor well-heeled foreign tourists sipping sunset cocktails.
The children are given $US1 to buy food or pencils or books following the performance, while the orphanage pockets $130 from a tour operator.
The founder of the orphanage spent months in jail before being acquitted of sexually abusing an 11-year-old girl under his care.
The centre's manager, Chanthou Thoeun, bows and brings his hands together at chest level in a traditional Khmer greeting, telling visitors they are free to interact with the children, whom he at first says are orphans, but when pressed admits most of them are not.
"The children go to school but there are difficulties finding enough money to buy food for them . . . there is malnutrition . . . we hope you can help us," he says, signalling that a donation is expected from visitors.
Ame, a volunteer in her mid-20s from California who has been living with the children for almost three weeks, sprawls on the floor of a bedroom watching cartoons on her smartphone with three children.
"I love the kids. This has been an incredible experience . . . I didn't know anything about Cambodia . . . the toilets have no paper and you have to squat," she says.
"I will be blessed when I return home."
Research shows volunteers like Ame usually leave orphanages feeling good that they have helped poor and abandoned children, and who probably showered them with affection.
But they will have almost certainly added to the psychological harm to the children, who become adept at appearing cute and engaging with strangers, behavior that is often mistaken for genuine friendliness and happiness
Fifteen year-old Ben Raksa, who has been at the orphanage for 10 years, says the children are taught to impress the strangers who arrive every hour or so because they donate money so that he and other children can be educated. .
Raksa says one Australian couple in their mid-50s took a group of the children for a beach holiday. "We were very happy," he says.
About a quarter of Cambodia's residential care centres are run by religious organisations, most of them with proselytising missions, adding to the difficulties of the children, who are often overwhelmed as they try to integrate back into a deeply Buddhist society when they leave the institutions.
The US-supported Foursquare Church, which runs 100 centres across Cambodia, resists the residential care label and the regulations that come with it, declaring on its website: "We do not run orphanages. We run churches, always have. Always will! And healthy churches care for the homeless."
A Phnom Penh Post reporter who visited one of the centres on an island in Cambodia's central Kampong Chhang province reported in late November that children were living in sleeping on torn mattresses in rooms that reeked of urine.
Sebastien Marot, executive director of Friends International, says one of the biggest concerns is the recruitment of volunteers from universities in Australia and other countries to work in orphanages.
A new Friends International campaign centres on the message: "Your donations don't help orphans - they create them," a blunt message to thousands of well-intentioned Australians who sponsor children, or spend weeks or even months working in orphanages or residential centres.
"Guys, stop. Think about what you are doing. This should not be about doing something so you can feel good about yourself," Marot says, adding that Australians should support programs that help keep families together, such as income generation and social support programs.
"Kids are dying in our hospitals every day through a lack of blood . . . why not help by donating some blood? Things like that," he says.