"They're made by kids as young as five," adds Dani Burrows. "And you can get 60 people working in a factory the size of your living room."

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The Myers Grove 12 and 13-year-olds are aghast, as one might expect.

But the message of the organisers of the 'Big Dress in Sheffield' weekend is to take their horror about the working conditions of the children who make their supermarket or High Street fashions – and then do something about it.

"We're saying they should write to their MPs and write to the companies," says Anna Piotrowska of the Speak network, organisers of the event.

"It's not about not buying cheap clothes, it's about ensuring there's a standard to make sure that these companies aren't allowed to do it any more."

The organisation cites the Companies Act of 2006, which enshrines certain responsibilities about social and environmental issues upon company directors and strengthens the requirements for companies to report on their (and their suppliers') environmental and social impacts.

Speak, along with other members of the Trade Justice Movement and Corporate Responsibility Coalition, say their campaigning helped to make the new act law.

The 'Big Dress' campaign is centred around a marquee made of thousands of pieces of patchwork made by people all over the UK. Participants in the Speak campaign have written and sewn messages of concern about the actions of big companies towards the people who make the products they sell.

The Big Dress now travels around the country to promote the campaign by Speak, which is a network of students and young adults who "pray and campaign on issues of global injustice".

The name, they say, comes from the verse in Proverbs which tells Christians to speak up for those who cannot speak for themselves and to defend the rights of the poor and needy.

The Big Dress was in Endcliffe Park last weekend and local campaigners joined in a festival centred around the campaign's themes of Fair Trade and campaigning for improvements to workers' conditions around the world.

On Monday, students from Myers Grove and All Saints secondary schools joined the Speak campaigners in a morning of workshops.

The teenagers wrote poems and a drama presentation about exploitation by multi-national companies and created recycled clothes on the theme of Fair Trade from a mountain of donated denim and other fabrics (and curtains).

"They're seeing the children that live and work in awful conditions making the clothes that they're wearing," says Laura Featherstone, a teacher at All Saints school. The school already has a Fair Trade tuckshop run by students. "There's a real enthusiasm about the issue," Laura adds.

"I hope coming here makes them even more motivated."

The marquee is full of campaigning material, displays and booklets urging youngsters to write to companies and organisations and MPs, even to adopt a multi-national and persuade the directors to change their ways.

Anna Piotrowska says: "We're trying to engage children with the idea of asking where their clothes come from. They're seeing that children their own age and younger might be working an 18-hour day on hourly ages lower than the wage they need to live on. They have to work those kinds of hours to make enough money to live."

"People should look at what they're buying and think about it and try to buy Fair Trade," says 12-year-old Louise Webster,

"We can make a difference," adds Dani Burrows. "Teenagers here who have I Pods and computers and phones should think about teenagers in Africa and India who are lucky to have a shelter to live in."