To see children's silhouettes at sunrise, bent as they chop canes with machetes, is to see the scale of poverty in Bolivia, where often every member of the family, no matter how young, has to work.
Fiser, 10, is one of Bolivia's many child labourers.
"I am not going to school any more. I left it this year when I started working here," he tells me.
His hands are covered in blisters and dark with a sticky dust after hours harvesting sugar cane.
Child labour is illegal in Bolivia, but it is estimated that almost a third of the country's children and adolescents (320,000) work in extreme conditions; in the mines, Brazil nut plantations and the sugar cane fields.
Boys like Fiser earn less than $5 a day during the six months or so that they work harvesting sugar cane, often from sunrise to sunset.
Such work is considered one of the worst forms of child labour by international bodies such as the International Labour Organization (ILO) and the UN children's agency, Unicef.
Ciro, 13, is typical. "I'd like to study or maybe work in something better, something lighter. But I work most of all for my family, my family is really poor so they have nothing and I need to help my six little brothers," he says.
"I wake up at four in the morning and come out to work until six in the afternoon, sometimes until eleven at night. The work is really, really hard."
Until recently, many farmers were moving away from sugar cane because they could get better, government-guaranteed prices for other crops, such as soya, rice and the local crop, coca - the raw material for cocaine.
But now, the price of raw sugar is hitting highs not seen for nearly three decades and farmers are switching back to sugar cane. Whole families are moving across Bolivia to work in the fields.
Sugar cane has a particular economic advantage: the harvest provides an income for a relatively extended period - roughly between April and November.
It is a way of making a living in Bermejo, a poverty-stricken area of south-eastern Bolivia on the border with Argentina.
Most of the heavy harvesting work is still done manually. Children aged between seven and 17 set crops alight to remove all unwanted foliage and then chop down the canes. Later, the top is cut off and the rest of the cane is stacked and loaded for transportation.
Luis, 13, started working three years ago.
"The work is hard, very hard, exhausting," he says. "The canes are heavy, cutting, chopping all day, last year I had a terrible back pain from work. I don't want to do this any more, but I have no choice."
About 60% of the sugar cane harvesters are temporary migrants from Bolivia's poorest areas. They live in shacks that are little more than mud huts, or under blue tarpaulins on the edge of the sugar cane plantations.
There is no hygiene; no privacy. As the local saying goes, they have "sweet canes but bitter lives".
"It is not a secret that children of all ages work in different conditions, in different sectors in this country," says Unicef's Bolivia representative Gordon Jonathan Lewis.
"As long as poverty exists, and the magnitude and the prevalence you have in a country like Bolivia, you will always have the need for children to contribute to households and local economies."
But in the sugar cane harvest, the exploitation of child workers can be extreme, Mr Lewis adds.
This view is echoed by Anastasio Rueda, a sugar cane trade union leader in Bermejo.
"Sometimes the boss takes advantage of them because they are young, and treats them badly. There are accidents. And of course there are children who do not want to come to work because the job is harsh, but some parents force them to," he says.
Now, nearly 20 years after the Convention of the Rights of the Child was agreed, Unicef is trying a range of ways to tackle child labour.
One is a "Child Labour Free" stamp for certain Bolivian products, like sugar. Together with Unicef, Bolivia's government has drawn up a plan to reduce child labour by 2015.
"The plans exists, the public policies are in place, the legal framework is there but right now we really do need a much more forceful approach," Mr Lewis says.
Some parents would prefer their children to be at school rather than in the fields. Unfortunately, money compels them to take their children into the fields with them.
That is the case for Fiser's mother, Angelica, who is working alongside him.
"He helps me a lot. He used to be at school but I need him to come to work with me, at least this year, then he can go back to school. Now we need the money so his little brothers can eat and go to school."
Angelica knows about the harsh reality of child labour herself as she has been toiling in the cane fields for a pittance since she was 10. She is now 44.
"Now he got used to work and he doesn't want to go back to school because he earns some petty cash and knows I need help," she says.
"But I tell him, even if it is a huge effort, he has to study so he doesn't end up like me, old and working in the sugar cane harvest. The children should have that opportunity. We are rotten already."