Child labour should never be taken lightly, but there is a widespread assumption that a bit of work in the fields is a normal part of growing up in impoverished countries such as Malawi, Bangladesh or Mexico. This notion of some sort of cultural acceptability serves to draw a veil over what is, frankly, abuse and the wrecking of children’s life chances. Child labour is never OK. But when children working boosts the profits of wealthy multinational tobacco corporations, it is an outrage.

It may be acceptable for children aged 13 to 15 to work in the tobacco fields, says the International Labour Organization (ILO), as long as the work does not have a harmful impact on their health or education. They are helping mum and dad. But this concept of happy families and cosy lives is an illusion. This is not a paper round after school, or learning needlework at a mother’s knee. The reality under the blazing sun, wielding a heavy homemade hoe, is very different.

The children working the tobacco fields. 'I wanted to be a nurse' Read more

If there are lots of reasons why child labour still takes place, there are absolutely no excuses when it comes to the tobacco industry. First, look at the crop. It is not groundnuts or bananas to eat, or cotton for clothes. It is something we are better off without. Tobacco is a product that will kill half of those who use it. That’s half of those in US and UK cities who have picked up the habit, some of them as children themselves. And it makes huge profits for multinational companies whose share price is solid. The market is gold-plated because the customers are addicted.

The work does untold harm in the field, ruining children’s chances of education and a better life. As part of a special report into the tobacco industry, I talked to a shy 14-year-old girl called Tiyamike, who laboured seven days a week alongside her family in the tobacco fields in Malawi. She knew the transformative possibilities of education, which the need to work had denied her. “You can become someone else,” she told me. “This is the importance of going to school.” She would have liked to become a nurse.

If they must stay in the business, they need to pay farmers more

Tobacco is a cash crop. Farmers like it because, at the end of a 10-month growing season, a field can sell for what seems like a large sum of money – maybe a few hundred dollars. Farmers dream of changing their lives with such a cash windfall. Maybe starting a shop. But it’s a gamble. They don’t know how much they will get until the harvest comes in. And the reality is that the family goes without until then, eating maize porridge and little else twice a day, and often runs up debts. It is vital that every member of the family works the fields – planting, weeding and, eventually, harvesting. With no money coming in, exercise books and pens are not part of the budget, and classroom time is abandoned.

The tobacco companies say they are doing all they can. None of them condone child labour. All say they have instructed their suppliers not to allow it and that they fund a variety of programmes to take children out of the fields and put them in school. But it isn’t working. In fact, the ILO says, child labour is increasing.

What more can they do? It is tempting to say stop making cigarettes, but that’s not on the cards. Even Philip Morris, which has pledged itself to “a smoke-free future” and has high hopes pinned to the success of vaping and “heat not burn” tobacco, has not offered to cease making Marlboros.

So if they must stay in the business, they need to pay farmers more. It is real poverty that stops families sending their children to school. The classroom may be free, but pens and paper cost money. So do uniforms. With better incomes, farmers could employ labourers rather than their own children. Higher wages might lure more people into tobacco farming, but there is only so much leaf ordered by “big tobacco” companies each year, so it would make little difference to production in the long run.

Ultimately, we should be campaigning against child labour of any sort in any country, from the textile sweatshops of Bangladesh to the brick factories of Peru. But in the tobacco fields of Africa and Asia, there can be no argument that hard labour does children – or the rest of us – any good at all.

• Sarah Boseley is the health editor of the Guardian