One of them, James Maea, 22, said the accident happened "out of nowhere".
"I heard a colleague call, 'Stop', but the van didn't stop at all and hit the kid. I think the driver didn't really know what he had hit. He kept driving until my boss told him to stop."
His colleague, Charlie Selui, went to the side of the van where the boy was lying, picked him up and put him on a couch that was on the side of the driveway.
Mr Maea said by that stage the boy was bleeding badly. "He had been here with his mum. She's a regular customer and she was inside looking at clothes and her child was running around [outside]."
The driver was distraught. "You could tell by the look on his face that he was sorry."
The boy's mother knelt in front of her son while another woman performed CPR.
The driver wiped blood from the face of the child, telling the mother, "Sorry, sorry".
Constable Amy Weston, of the Counties- Manukau serious crash unit, said it was too early to say if the driver would be charged but urged witnesses to come forward.
The child's death followed the fatal crash in Cambridge at 8.20am in which the 40-year-old mother drove through a stop sign at the busy Cambridge Rd/Kaipaki Rd intersection and was hit by a tar truck.
She was just about to drop her son at a school holiday programme. He was taken in a critical condition to Waikato Hospital, then transferred to the Starship in Auckland.
The truck driver, travelling from Te Awamutu to Mt Maunganui to collect bitumen for Blacktop Construction, was in shock.
Chris Rasmussen, who runs the Kid Zone school holiday programme in Te Awamutu, said the boy had been attending for about two weeks. A shuttle bus had just picked up a couple of children from the Cambridge Town Hall and was on its way to collect the boy when it came upon the crash.
Mr Rasmussen said the bus returned to the centre and the children in the holiday programme spent the morning writing get-well cards for the 9-year-old.
Waikato road policing manager Inspector Leo Tooman said it was too early to know whether the car had come to a halt at the stop sign, but the truck had right of way.
It was the fifth fatal accident in the Waikato this year. "You hit a truck, you are probably going to die," Mr Tooman said. "They are very unforgiving."
Safekids New Zealand director Ann Weaver said the Manurewa fatality wasn't a typical driveway incident, but the message the injury-prevention service was trying to convey was that children and cars do not mix.
"Parents and caregivers do need to be vigilant around cars, and that includes anywhere there's an opportunity for a car and a child to be together."
Ms Weaver said it would be helpful if shops like the ones in Dalgety Drive would get together and put up signs warning motorists of children.
On average, about six children die in non-traffic pedestrian events each year, and for every child killed by a vehicle moving at low speed, about 12 are admitted to hospital.
Anyone with information about the toddler's death is asked to call Counties-Manukau police on (09) 261-1300.
