Image caption Some 400,000 children work on cotton farms across India

Rada estimates she is 11 years old, but she can't be certain. She says she has been working in the Indian cotton fields for three years.

"My parents stopped me going to school because they needed me in the fields," she says.

"I picked the male flowers and rubbed them on the female flowers. I also had to weed the fields.

"First of all they sent me to other farms to work. I earned 120 rupees a day. Next year I am going to work on my parents' field."

Rada, who comes from Andhra Pradesh in south-eastern India, goes to school at the moment but many other children do not.

It is estimated more than 400,000 children under the age of 18 work on cotton farms across India.

According to the most recent study by the International Labor Rights Forum in the US, half of them are younger than 14.

Their main role is to cross-pollinate crops by taking the stamen of the male plant and rubbing it onto the female plant. It is a laborious task, but it helps farmers to get a better yield.

Many of them prefer to employ children because they have nimble fingers and are the same height as the plants.

'They work as we tell them'

The Indian government says the number of children aged between five and 14 who are working in the fields is going down.

I worked from eight in the morning until eight at night. I almost did not realise when my hand got pulled in. It was oozing a lot of blood so I got some cotton and pressed it on my hand before running out Sonal, aged 16, cotton mill worker

Delhi is working to improve this further by creating an environment where families do not need to send their children to work. But the use of child labour is very evident to anyone driving through the cotton fields of rural India.

"We used to have a lot of children working. They work as we tell them," says Venkatram Reddy, a farmer in Andhra Pradesh.

"Sometimes it rains. We give them plastic sheets and they put them on their head and carry on working.

"It is not possible with adults. They don't work as hard and don't come on time. Although we pay them both the same wages, it is children who work sincerely and honestly.

"And it is the girls who work much better than the boys. The boys are always running around. If you beat them they stop working. We used to have lots of children and girls mainly. Now there are more adults.

"We stopped because many people are threatening that we should not have child labour and that we will face troubles," he says.

In the UK, all retailers have codes of conduct to prevent poor working conditions and child labour in the supply chain.

UK retailers generally buy completed garments. They sign agreements with the manufacturing factories to guarantee conditions, but it can be difficult to trace the origin of the raw materials.

Cotton can be traded dozens of times before it reaches the final factory. The traders buy from various sources and the cotton is often mixed in mills.

So it is often almost impossible to trace a bale of cotton to a mill, let alone back to a single farm.

'They won't allow access'

Image caption Sonal lost her hand in a cotton mill accident

There is also concern over working conditions in the mills.

"Since 2005 the total number of children in the mills has gone down," says Priti Oza from the Prayas Centre for Labor Research and Action, who has spent most of her life trying to improve working conditions in India's mills.

"Large numbers of children still come here from neighbouring Rajastan, though.

"They do not register the labour and they won't allow access to outsiders. So it is very hard to check."

Sonal is 16 years old. She lives with her parents and four brothers and sisters in a house with two rooms in a small village in rural Gujarat.

Last year she lost her hand in a machinery accident at the mill she worked in.

"I worked from eight in the morning until eight at night. I almost did not realise when my hand got pulled in.

"It was oozing a lot of blood so I got some cotton and pressed it on my hand before running out."

Sonal was given some medical support and paid 100,000 Indian rupees ($1,600; £970) but she won't be able to work again and will get no more financial help.

Western pressure

In the UK, the British Retail Consortium says there have been significant improvements within the garment and textile supply chain, and that British retailers and consumers are concerned by reports of persistent human rights violations in some parts of the cotton industry.

Firms such as Marks and Spencer, John Lewis, H&M, Ikea and Sainsbury say they are working alongside various organisations like Fairtrade, the Better Cotton Initiative and Cotton Connect to improve conditions for farmers and to make the supply chain more transparent.

Image caption It is often almost impossible to trace a bale of cotton to a particular mill or farm

While pressure from the West is making a difference to the cotton supply chain in India, there is not the same pressure from within the country.

Rampant poverty, high inflation, unemployment and a lack of regulation of the industry makes it difficult to see how or why people will change.

There is another problem too. As the country's wealth gap increases, the growing Indian middle class is buying more clothes, and the fear is they won't share Western concerns about the supply chain.

You can hear more on this story on You and Yours at 12:00 GMT on BBC Radio 4 all this week.