Pupils tell us whether they care where their clothes come from
Fashion chain Primark, which is best known for its cheap clothing, says it's "extremely concerned" about the findings and is carrying out its own investigation into what's been going on.
A BBC undercover reporter who got a job at the factory said it was cramped and unsafe, with boxes blocking corridors and toilets, and in some areas it was so cold staff were working with their coats on.
She said lots of people told her they worked 12 hours a day, seven days a week, and some of them even admitted working illegally as they don't have permission to work in the UK.
Last year, another BBC investigation found kids in India were making clothes for another company that supplies Primark.
What's shocked people about THIS investigation though is that the sweatshops are in the UK.
Neil Kearney from the International Textile Worker's Federation, which looks after workers' rights, says the findings are a "total scandal".
"There's no such thing as cheap clothing," he said. "Somebody has to pay and in this case it's the workers in Manchester."
Until Monday, Primark had posters in its shop windows saying it believed in ethical trading, but now they've been told to take them down.
It says its clothes should be made in safe and hygienic conditions and has apologised for any harm and distress that's been caused to the workers in Manchester.