The company did not name the offending factories, or say where they were based, but the majority of its goods are assembled in China.
Apple also has factories working for it in Taiwan, Singapore, the Philippines, Malaysia, Thailand, the Czech Republic and the United States.
Apple said the child workers are now no longer being used, or are no longer underage. “In each of the three facilities, we required a review of all employment records for the year as well as a complete analysis of the hiring process to clarify how underage people had been able to gain employment,” Apple said, in an annual report on its suppliers.
Apple has been repeatedly criticised for using factories that abuse workers and where conditions are poor. Last week, it emerged that 62 workers at a factory that manufactures products for Apple and Nokia had been poisoned by n-hexane, a toxic chemical that can cause muscular degeneration and blur eyesight. Apple has not commented on the problems at the plant, which is run by Wintek, in the Chinese city of Suzhou.
A spokesman for Wintek said that “almost all” of the affected workers were back at work, but that some remained in hospital. Wintek said n-hexane was commonly used in the technology industry, and that problems had arisen because some areas of the factory were not ventilated properly.
Last year, an employee at Foxconn, the Taiwanese company that is one of Apple’s biggest suppliers, committed suicide after being accused of stealing a prototype for the iPhone.
Sun Danyong, 25, was a university graduate working in the logistics department when the prototype went missing. An investigation revealed that the factory’s security staff had beaten him, and he subsequently jumped to his death from the 12th floor of his apartment building.
Foxconn runs a number of super-factories in the south of China, some of which employ as many as 300,000 workers and form self-contained cities, complete with banks, post offices and basketball courts.
It has been accused, however, of treating its employees extremely harshly. China Labor Watch, a New York-based NGO, accused Foxconn of having an “inhumane and militant” management, which neglects basic human rights. Foxconn’s management were not available for comment.
In its report, Apple revealed the sweatshop conditions inside the factories it uses. Apple admitted that at least 55 of the 102 factories that produce its goods were ignoring Apple’s rule that staff cannot work more than 60 hours a week.
The technology company’s own guidelines are already in breach of China’s widely-ignored labour law, which sets out a maximum 49-hour week for workers.
Apple also said that one of its factories had repeatedly falsified its records in order to conceal the fact that it was using child labour and working its staff endlessly.
“When we investigated, we uncovered records and conducted worker interviews that revealed excessive working hours and seven days of continuous work,” Apple said, adding that it had terminated all contracts with the factory.
Only 65 per cent of the factories were paying their staff the correct wages and benefits, and Apple found 24 factories where workers had not even been paid China’s minimum wage of around 800 yuan (Pounds76) a month.
Meanwhile, only 61 per cent of Apple’s suppliers were following regulations to prevent injuries in the workplace and a mere 57 per cent had the correct environmental permits to operate.
The high environmental cost of Apple’s products was revealed when three factories were discovered to be shipping hazardous waste to unqualified disposal companies.
Apple said it had required the factories to “perform immediate inspections of their wastewater discharge systems” and hire an independent environmental consultant to prevent future violations.
However, Apple has not stopped using the factories.
In 2008, Apple found that a total of 25 child workers had been employed to build iPods, iPhones and its range of computers.