The children, aged four and five, opened the door to a caretaker after a bad smell from the apartment was picked up.
The dead man might have been their father, but this still needed to be confirmed, police said.
Boschkop police spokesperson Captain Marissa van der Merwe said a gardener at the complex became aware of the bad smell around 16:30.
He reported the smell to the caretaker who investigated.
“The caretaker looked through a window and saw two children inside the flat – one of four years and the other of five years old.”
He asked the children to open the door.
Van der Merwe said: “The caretaker found a decomposing body of a man and immediately called the police.”
