Matthew David Molloy had been driving at about 96 km/h in a 70 zone in the lead up to the rear-end crash in Perth on December 29 last year, which shunted the front of the van underneath a truck.

Leonardus Tjandra suffered catastrophic head injuries while six members of his family, including his six-year-old brother Franciscus, suffered serious injuries.

Molloy, 36, who was disqualified from driving for life at the time of the crash, did not take any evasive action, fled the scene and called his mother to pick him up nearby.

He claims he cannot remember the crash.

In the District Court of WA on Tuesday, the boy's father Edwin Tjandra delivered an emotional victim impact statement, saying his life had been ruined.

He said he had never thought his son would be suddenly taken away from him at such a young age by someone who had just got out of prison.

"There is no happiness in the house. It is quiet now - no different to a cemetery," Dr Tjandra said.

He said he suffered flashbacks from a multitude of reminders and couldn't stop weeping when he once had to go past the scene on Leach Highway in Wilson.

"I break down at the slightest trigger," he said.

"Christmas is all about tragedy now."

Dr Tjandra said his other son had asked "why he could not die as well".

On top of the emotional pain, the court heard the victims still suffered from their injuries including suicidal thoughts, constant discomfort, ringing ears, broken teeth and the need for further surgery.

Since the age of 14, the longest stint Molloy had outside of prison was four months.

Judge Bruce Goetze said he had become institutionalised, with a 41-page criminal record including multiple car theft offences.

Molloy's dysfunctional childhood included being taught by his father to inject heroin at age 13.

He took the drug the day before the crash, having relapsed after being released from jail just over a month prior.

Defence counsel Jim Brash said his client was deeply remorseful for the crash and felt sorrow for the family but could not explain why it occurred.

Outside court, Dr Tjandra said Molloy should have received the maximum sentence for dangerous driving causing death of 20 years.

He said his son's life was worth more.

"What kind of message is this court sending to society? If you are parents, you will share my opinion," he told reporters.

"He's more than capable of offending again."

Dr Tjandra was also dismayed Judge Goetze raised the possibility of Molloy having yet another lifetime driving ban overturned.

Molloy will be eligible for parole after serving five-and-a-half years.

Australian Associated Press