It is illegal for children younger than 15 to work long hours or do heavy labor, and the government says it is trying to provide education and help to families so they do not have to send their children to work at the kilns.

The use of child labor is also a concern of NATO forces in Afghanistan, particularly those involved in reconstruction programs. Yet kiln owners and contractors say bricks made by children are routinely used in NATO projects.

A spokesman for the international security force in Afghanistan, Lt. Bashon W. Mann, said that the force conducted frequent inspections at construction sites and that the coalition had no knowledge of having used building materials made by children.

At the kiln where Nick Muhammad works, his father, Zar Muhammad, 55, said he was haunted by guilt that his children would inherit his debt. His two youngest sons, Gul, 7, and Neyaz, 8, worked beside him in the mud as he spoke.

Neyaz’s hands fly with astonishing speed. But the boy looks worn down, exhausted by 12-hour days that start before dawn.

“I don’t like this job,” he said. “I want to go to school and to become a doctor to serve my people and my country.”