"As a parent, I know that this type of incident is every parent's worst nightmare; you're left with all these 'what ifs'," Ms Grace said.
"It's important to ensure that when children are riding, they are safe, and high-visibility clothing and helmets are a must to prevent injury."
The police serious crash unit is investigating the incident.
Lillian Bond lives across the road from where the accident occurred and was the first to call 111.
"I heard a loud bang and then a child screaming. It was a freak of an accident.
"The car wasn't going any more than 5km/h as it backed out of the driveway, but the boy was really stuck under it after it hit him.
"I heard the scream and looked out my window. It looked like he was trying to catch up to his sister, who was in front of him."
The Raglan Fire Service was quickly on the scene -- its base is nearby, on Wainui Rd -- and set about lifting the car off the boy.
Ms Bond said it took half an hour for the boy to be freed.
"They were using trolley jacks and wedges to try to get him out.
"I had to move away from the window after a while; I didn't want to watch anymore."
Fire officer Dirk De Ruysscher was in charge of the crew lifting the car off the boy.
"It was a bit of a tricky situation. We had to be careful the bike didn't interfere with what we were doing," he said.
When the Fire Service arrived, a group of bystanders were attempting to free the boy using a jack borrowed from a nearby garage, but it was not proving sufficient.
"We had to remove a wheel on the car to make more space for the boy to get out."
Mr De Ruysscher said the boy remained calm during the rescue.
"You never expect things like this, but overall I'm glad we could get him out.
"He was pretty calm. We talked to him and tried to connect with him. He was as okay as he could be, I suppose. He was responsive. He was responsive when he was freed as well."
Mr De Ruysscher was grateful for the help from the people immediately on the scene.
He said having the Raglan fire station so close by was also beneficial.
"It helped us being quick to the scene, but at the same time all the [firefighters] are volunteers, and they're working during the day, which can make it hard to respond quickly."
Ms Grace urged motorists to take extra care tomorrow, when a a number of schools across the Waikato welcome back their first students.
"Many of them will be sharing the road with motorists, riding bikes or as pedestrians, and we ask drivers to be mindful of this."
People needed to be particularly careful over the Auckland Anniversary weekend, Ms Grace said.
"We all want to reach the beach this holiday weekend, so when out riding, driving or walking, our advice is wear the appropriate safety equipment and check, then check again."
