Ekhuruleni metro police described a video showing a man riding a motorcyclist with a toddler on the back in Edenvale as "horrifying".
The video went viral this week, sparking outrage and concern over the child's safety.
The man is seen riding the bike at high speed and ignoring a red robot.
The child, meanwhile, clings on with a bicycle helmet on her head.
The police's Wilfred Kgasago said that the incident was being investigated.
"It was horrifying, detestable, despicable the way this guy has behaved. I don't want to pre-empt things, but we have decided to take the video [and] to go to the prosecutor so that he can advise us," said Kgasago.
Watch the video here.