Orphaned NSW boy still critical

Orphaned seven-year-old Benjamin Milne remains in a critical condition at a Sydney hospital as police investigate a crash that killed his parents and older brother.

The Milne family had left for a day trip to the beach on Sunday when their car veered off the road travelling at 90-100 km/h and hit a tree on the NSW Central Coast.

Darren, 42, and Susana, 39, and Liam, 11, were killed instantly.

Benjamin remains in an induced coma at Westmead Children's Hospital, where he's expected to undergo surgery on Tuesday, police said.

Police are investigating whether the crash was deliberate.

The lack of any signs of braking before the fatal smash and absence of witnesses led police to search the family's Ryde home in Sydney's northwest on Monday.

It is understood police did not find a suicide note but were seen removing other material from the house.

Police had initially suggested inattention could have been the cause of the crash as there was no "savage movement" before the car went off the road.

Police had trouble locating Benjamin's next of kin, including the family of the boy's mother, who are in Mexico.

The boy's aunt has reportedly rushed to the hospital while news reports say Mr Milne's father is travelling to Sydney from Myanmar.