Three children died when their shack caught alight in Kagiso, on the West Rand on Thursday morning, Gauteng police said.
The brothers, one aged four and twins aged one, were "burnt beyond recognition and were confirmed dead at the scene", said Warrant Officer Solomon Sibiya.
The landlord of the shack the boys lived in with their parents discovered it was in flames and alerted her neighbours.
"She screamed for help and her neighbour arrived with water and sand in an attempt to extinguish the fire," said Sibiya.
However, the neighbours and firefighters called to the scene were unable to extinguish the fire in time to save the children.
The boys were alone in the shack at the time.
The cause of the fire was unknown and an inquest docket had been opened.