The truck that overturned was carrying Afghan families returning from Pakistan, where they had been living, according to a spokesman for the governor of Laghman province.
20 people have died - five women, three men and 12 children, he says.
Fatal traffic accidents are common in Afghanistan, partly due to dangerous driving, a lack of regulation and poor roads after decades of conflict.
The accident occurred in eastern Afghanistan, on the road between Jalalabad and the capital, Kabul.
