Italy's financial police also found a 14-year-old and a 17-year-old working at the Chinese-owned factory in Olgiate Olona, a town in Varese province, Corriere reported.
The police found the child workers, who were assembling parts on leather products for well-known fashion brands, during a routine inspection. All three were the children of staff members.
Police have carried out 16 factory inspections in recent months, during which 22 people were found to be working illegally, including eight foreigners.
Some 100,000 products were also seized due to safety violations.