Student interns worked in the Yantai factory for approximately three weeks.
Foxconn, the Taiwanise electronics maker most famous for being Apple's biggest manufacturing partner, has admitted to putting students aged between 14 and 16 to work at its factory in Yantai, reports the guardian.
"Our investigation has shown that the interns in question, who ranged in age from 14 to 16, had worked in that campus for approximately three weeks," the company said, but did not state the number of under age workers.
"This is not only a violation of China's labour law, it is also a violation of Foxconn policy and immediate steps have been taken to return the interns in question to their educational institutions."
Foxconn makes products not only for Apple, but also manufactures PlayStation 3s, Xbox 360s and Kindles.
The firm made the announcement following an internal investigation instigated because of Chinese media reports of underage interns.
No evidence has been found of related violations in Foxconn's other factories.
"We recognise that full responsibility for these violations rests with our company and we have apologised to each of the students for our role in this action," the company said.