Wal-Mart wants suppliers to list exactly which factories they work with. The retail giant says it will cut ties with anyone who subcontracts work without permission.

The report on supplier responsibility from Apple indicates progress on working conditions and excessive overtime requirements at the tech giant's Chinese suppliers, including its largest supplier, Foxconn. But the report also revealed one supplier was employing child workers.

Nearly a quarter of a billion Chinese workers relocated from the country's interior to the factory towns on the coast in one of the largest human migration the planet has ever known. Now, 20 years later, the great migration is drawing to a close.

Marketplace's Rob Schmitz was offered a rare glimpse into the world of Apple's usually secret supply chain. Here's the story of the people who help run Apple's Chinese producer, Foxconn.