Wal-Mart Stores Inc. uses Chinese factories that deny workers overtime pay and maternity leave and pays them less than the local minimum wage, according to three reports released yesterday by labor monitoring groups... Lungcheong Toy factory [part of Lung Cheong International] in Guandong Province in southern China employs laborers younger than 16, the legal age limit, another report says. Workers at the factory, which also makes goods for Mattel...must sign forms saying the factory owner is not responsible for on-site injuries, according to the report... Wal-Mart says it has been aggressive in detecting and correcting labor problems in suppliers' factories... Bill Wertz, a spokesman for...Wal-Mart [said] "We and other retailers have very strict programs in place, and we do our very best to enforce standards in factories that we don't own"... [also refers to Guangzhou Huasheng, Panyu United]