Karabo Khumalo, 10, was walking with his mother, Johanna, in Bela-Bela, Limpopo, on Tuesday evening when a police Nyala drove past and an occupant shot at them.
Karabo was hit twice - once in the head - and died in hospital on Wednesday.
"This is wrong; we are very angry as a family," said Abraham Chokwe, Khumalo's uncle.
"They shot and killed Karabo and no one is talking about it."
The community this week took to the streets to protest against electricity price increases and what they believed to be the suppression of a report on corruption.
Chokwe said the young boy was a gifted footballer and "loved going to school". He said Khumalo was not part of the protest and the police visited the family only after news of his nephew's death became widespread.
Independent Police Investigative Directorate spokesman Moses Dlamini said the shooting had not been reported immediately .
"The discharge of an official firearm was not reported to Ipid. The failure to report this will also be investigated," he said.
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