According to the Community Emergency Response Team (CERT), a team of volunteer first responders, the strong current pulled the vehicle into the river.
Emergency services and the volunteers spent hours trying to find the vehicle.
CERT spokesperson Riza Sadack said the search had to be called off on Monday night because it had become unsafe and weather conditions were bad.
When the search resumed on Tuesday morning the vehicle was found.
Sadack said the children were missing. It is understood the grandmother was in the vehicle.
CERT rescuers were dispatched to La Mercy, north of Durban, on Tuesday morning where a wall collapsed leaving one person dead.