Rodrigo Medrano Calle is a Bolivian labour leader who meets and lobbies top government officials for his constituency's rights. That's not surprising in a country where pay is often low, working conditions harsh and unions play a powerful role in society. What's unusual is that Rodrigo is just 14 years old, and his union's members are all children

"I started working when I was nine, and I've done everything, shining shoes, bus driver's assistant, selling. I've gone through most of the jobs common for child and adolescent workers," said Rodrigo, who now sells chewing gum and cigarettes in bars at weekends, making £4-£5 for a night's work. "I lived on the street for a time and was going in the wrong direction, but then I found the movement, and it gave me a reason to be. I'm going to fight for my compañeros' rights, not just my own."

Rodrigo's organisation, the Bolivian Union of Child and Adolescent Workers (Unatsbo), represents thousands of under-18s, in seven of the country's nine departments. And it's not just a Bolivian phenomenon: there are similar chapters in Guatemala, Paraguay, Peru and Colombia. Often funded by international donors, the organisations seek to bring young workers together to defend their rights and promote education. In Bolivia, successes include organising pay rises for children who sell newspapers on the city streets of Potosí from 6 cents (½p) to 12 cents a paper, using negotiations and the threat of strikes.

Many international campaigners advocate an end to all child labour, but Unatsbo follows a more pragmatic line, arguing that, in a region where child labour is rife, it is more important to ensure young workers are not exploited. On paper, Bolivia bans under-14s from working, but nearly 750,000 children aged between five and 17 are involved in sometimes dangerous jobs.

Luz Rivera Daza, an adult counsellor for Unatsbo in Potosí, says many child workers are in a legal blindspot: their work is prohibited and so they have very little defence if employers exploit them through long hours, physical or verbal abuse or refusing to pay a decent wage. "If you have to work, then you have to work exploited," she said of those situations. "This just makes you more vulnerable."

Bolivia's informal economy includes everyone from bricklayers to farmers to shoeshiners, who work without contracts and set schedules. Many adults are part of this market, as are the great majority of child and adolescent workers. These young workers seem to be everywhere – in the cities they pack groceries at the supermarket, shine shoes on pavements, collect fares on buses, and sell cigarettes and sweets late at night in smoky beer halls. In the countryside they help their parents in the fields, herd sheep and llamas, or do the brutal work of mining or the sugar cane harvest.

In a country where poverty is widespread and the minimum wage is $150 a month, living expenses can overwhelm a family, especially if one parent works. That was the case for Delina Juárez Mamani, whose son, Rolando, began helping her sell used clothes at a market stall in the city of El Alto when he was 12.

"I never brought my children to work," she said. "Then the father left us and since then my kids come because I need the help." Rolando, who is now 17 and a Unatsbo leader himself, puts together the large metal frame and tarpaulin structure of her shop, and makes a little money helping others do the same. He works two long days a week, and that money pays for his transport to and from school. Juárez Mamani believes combining a job and school can be hard on young people because they may be tired from working, but says that education is a top priority for her children. In fact, most working children and adolescents in Bolivia also go to school.

Rodrigo believes that instead of attempting to end many forms of child and adolescent work, the goal should be ending exploitation by creating part-time, safe and better paying jobs for young people who want them. "Why should there be a minimum age if the work is voluntary?" he asked. "The work of a child or adolescent is not bad – it helps society, it helps a family, and it helps us grow as people."