The International Labour Organisation has described the practice of children working in Cambodia's salt fields as "one of the worst forms of child labour", and the Cambodian government has signed up to stop it. So why is the practice continuing?
Work in the salt fields is hot and intense
Work in the salt fields is harsh and unpleasant, even for the adults involved. But it is particularly hard for children.
"It is very difficult work, but I have to do it for the money," Roh, a 16-year-old salt carrier, told BBC World Service's One Planet programme.
Child labour is commonplace throughout Cambodia, in industries such as manufacturing, construction and the restaurant trade.
In total the Cambodian government estimates that 1.5 million children are working in Cambodia - about a quarter of the child population.
However it is their work in the salt fields that is causing particular concern.
The work involves distilling salt from sea water into smaller pools. The heat is intense and the pools reflect the sunlight.
Roh carries salt for four hours in the morning, and then for another three hours in the afternoon.
When he was younger he attended school for two years - but now, he says, he does not have time.
"I was worried that my parents worked so hard, so [now] I help them," he said.
"My father is old, and he is not strong enough to do all the heavy lifting. So I have to help him."
Roh's seven brothers and sisters also work in the salt fields - and they are far from alone.
Fourteen-year-old Chaii Soph Heap has worked in the fields for three years. In addition to his job, he attends school for one hour each day.
His family are comparatively wealthy - his father, Chi Vannaranna, owns his own land.
But Chi Vannaranna argues that he could still not afford for his children to stop working.
"The children help me in the salt fields because it provides them with a skill, and it helps the family to get an income," he told One Planet.
"I still send my sons to school, because their education is very important too.
"The work is hard, and it's hot, but the children understand that they have to help the family.
"If my family were rich, I wouldn't ask my sons to work there. I have to force myself to let the children work in the salt fields."
MP Joseph, who heads the International Labour Organisation's programme for the elimination of child labour in Cambodia, explained that 80% of child labour occurred in rural areas, predominantly in agriculture, but also fishing, brick-making and, of course, the salt fields.
All these sectors are important for Cambodia's economy.
The United Nations' Minimum Age Convention states that the youngest age for "light work" should be 13, while for ordinary forms of child labour it is 15.
Salt field work is exceptionally harsh, and would not be tolerated in the West - leading to accusations that different rules are being applied in poorer countries.
The ILO favours a gradual approach to the elimination of child labour, introducing "non-formal education" - a few hours of schooling a week.
In theory schooling in Cambodia is free, but in practice this is not the case, as transport, books and paper all have to be paid for.
Added to that is the fact that if a child is attending school, they cannot earn money.
Mr Joseph admits this is a problem.
"Personally, if it were possible, I think every child should go to school - there can be no compromise on that," he said.
"It's not a child's place to work. You don't see puppies working for dogs, you don't see lion cubs working to feed the lions. Why should human beings send their children to work?
"I think it's against nature. It's contrary to humanity. But then, in a situation where children are already working, the transition may take time."