A Daily Mirror exclusive reports kids as young as 5 forced to break rocks and repair railways.
A network of brave informers used hidden cameras to secretly record footage over the course of this year.
In one film – shot in the north east province of Ryanggang – a forlorn lad of around eight or nine, wearing an England football shirt, is ordered to break rocks at a cliff face.
Girls pair up as they struggle to lift heavy loads into piles. One young boy winces under the strain of his work.