The five were apparently trying to burn wet straw when the shack ignited, China's state-run Xinhua News Agency reported.
Four of the boys, ages 4-6, were dead when authorities found them. The fifth boy died later at a hospital.
The children had been left on their own while their parents helped a local villager with a wedding, the South China Morning Post reported.
The shack, located in southwestern China's Guizhou province, had been used to process tobacco at one time. It had poor ventilation and only one exit, the newspaper said.