The baby died from her injuries at Starship children's hospital early yesterday.
She was sitting on her mother's lap in the back seat of a Honda hatchback that slid across SH4 and hit a bank south of Te Kuiti on Monday about 8.30am.
All six passengers in the five-seater car, including the baby girl's 3-year-old sibling, were wearing restraints - except for the infant, whose car seat was later found by police in the boot.
The crash is one of a string of accidents which has marred Road Safety Week.
Waikato district road policing manager Inspector Freda Grace said the most tragic aspect of the baby's death was its avoidability.
"Police staff located a car seat unused in the car's boot that possibly could have prevented the baby suffering the critical injuries," she said.
"Sadly, with so many people in the car there wasn't room to fit it."
Safekids director Ann Weaver said she was shocked that parents were not heeding the law and agencies such as her own, and the likes of police, Plunket and the NZ Transport Agency which were trying to promote a message of child safety in cars, were still not getting through.
"It's been proven over and over again how well a car restraint can save a child in a crash and I just don't understand how parents cannot continue to protect their children.
"We are still seeing these cases of injury or death as a result of someone not thinking it could happen to them."
It is not clear whether anyone will face criminal charges as a result of the baby's death.
"It is a police issue. However, we do have a law that says children have to be in an appropriate car restraint until they are 7," Ms Weaver said.
"Looking at it from the child's perspective, they have the right to be protected ... and that's what we need to advocate in incidents like this."
The little girl's death came on the day a 22-year-old woman was killed near Ohaupo, south of Hamilton, when her northbound yellow Mazda car crossed the centreline and collided with three southbound vehicles including a truck.
The woman was the sole occupant and died at the scene while another person from one of the vehicles was taken to Waikato Hospital with minor to moderate injuries.
In Hawkes Bay on Monday, 25-year-old Hina Kerei Johnson Hamahona died after smashing through a crash barrier protecting the approach to a bridge near Havelock North. Mr Hamahona is believed to have made a final telephone call to his family while trapped in the wreckage.
On Sunday, brother and sister Shannon and Danielle Kiriau died in a high-speed accident in Dunedin in which none of the back-seat passengers was wearing seatbelts.
Horror run
Monday 5.50pm: Woman dies on SH3 near Hamilton after crossing into oncoming traffic while overtaking.
Monday 8.30am: Unrestrained baby thrown from mother's lap in crash on SH4 near Te Kuiti. The baby died yesterday.
Monday 4.15am: Hina Hamahona dies after smashing through a crash barrier near Havelock North.
Sunday, 3.30pm: Woman dies after being hit by a reversing car.
Sunday 3.15am: Shannon and Danielle Kiriau die in high-speed accident in Dunedin.
- James Ihaka, NZ Herald
