A toddler has died after being hit by a family car while on a roadside toilet break, in what appears to be tragic accident in regional South Australia.

The boy's mother, who was driving the car, pulled over on the remote Port Davis road near Port Pirie at 11.30am on Sunday so her two-year-old son could have a toilet break.

When the mother got out to assist her son, it appeared the car rolled forward and hit the child, Sergeant Steve Griggs from SA Police said.

"It would appear that the vehicle was still in drive, and as the driver got out to assist the child, the vehicle moved forward," he said.

"It very tragic and devastating set of circumstances, for the family and community. It will hit deep in the local community."

Paramedics were unable to revive the boy, who died at the scene.

The boy's mother was taken to hospital in shock. Her younger daughter, who was in the car at the time, was unharmed.