All but one member of a family have been killed in a car crash on the Central Coast on Sunday.
Police believe the 42-year-old father may have turned around to speak to his young children, causing the silver Toyota Corolla to crash into a tree at Fountaindale.
The sole survivor, a seven year-old boy, was in a critical condition in hospital, fighting for his life, after both his parents and brother, 11, were killed.
Police said the family were heading north from Sydney when the accident occurred on a straight stretch of Enterprise Drive, between Wyong and Lisarow, about 12.20pm.
Crash scene investigators pored over the scene looking for clues as to what may have caused the car to veer off the road and hit the tree head-on.
Inspector Colin Lott of the Tuggerah Lakes Local Area Command said witnesses told police the car was travelling between 90 and 100km/h in the 90km/h zone and did not appear to brake as it veered off the road.
"It hit the tree at full speed," Inspector Lott said.
He said the most likely cause of the crash was inattention.
"It was not a savage turn and the car was only a few metres off the road," Inspector Lott said.
"Most likely the driver turned to speak to the children."
The driver was dead when emergency services arrived.
A female passenger, 39, died shortly after. The two boys were pulled from the back seat.
The older child, 11, died of cardiac arrest in the ambulance while the youngest child was flown to The Children's Hospital at Westmead, where surgeons were waiting to operate.
A report will be prepared for the information of the coroner.
