Nearby resident Aaron Stevens said the road was notorious because driveways exited on to a very busy and bendy stretch of road.
"With that speed and with people pulling in and out of properties, it's not safe. I have nearly collected cars, people and pets out on that road."
Detective Slade Sturmey of Levin CIB said the crash happened at a location known as Marycrest.
A northbound white car was stopped on SH1 indicating to turn right into a private driveway, he said. A small truck ploughed into the back of it, pushing it into the southbound lane, where it collided with a car coming the other way.
The 10-year-old boy was undergoing surgery last night.
A 7-year-old girl has spinal injuries and injuries to the remaining occupants were not believed to be life-threatening.
Two people in the truck and another two in the other car were treated at the scene.
Meanwhile, a 31-year-old pedestrian was hit by a car and killed early yesterday in the coastal Nelson suburb of Atawhai.
And a child was seriously injured on Maraetai Coast Rd near Clevedon yesterday afternoon, after being struck by a bicycle or motorbike.
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Vehicle rolls, man dies
Frantic efforts by a group of off-road enthusiasts failed to save the life of a passenger in a Toyota Land Cruiser which dropped 35m off a bank on farmland in Ruakituri, near Wairoa.
Gary Grayson, 72, and Mike Finlayson, 69, were on a three-day fundraising safari with 117 other drivers when the vehicle rolled about 2.30pm on Friday.
Organiser Mark Harris said a group of people, including two nurses, spent 90 minutes keeping Grayson conscious.
Grayson later died in the rescue helicopter.
Finlayson remained in a serious but stable condition at Hawkes Bay Hospital.