Peter Watfa, 43, has pleaded not guilty to the child's manslaughter after his BMW crashed close to his Liverpool home in Lurnea on February 25, 2019.

Prosecutor Ken Gilson outlined the crown case to the jury in the NSW District Court on Tuesday, saying shortly after the crash Watfa emerged from the driver's seat with the baby in his arms.

The child had a "distinctive bruise on his cheek," and later died in hospital from internal injuries.

"It is a tragic case," Mr Gilson said.

The near-head-on collision was caused by a Mercedes driver coming in the opposite direction attempting to turn right too early at an intersection, according to the crown case.

Watfa told a bystander at the scene that the child had been strapped into a back seat baby capsule, a story he "maintained" later at the police station.

But the Crown argues that had the baby been securely strapped into his seat, there was "no possibility" he could have sustained the fatal injuries.

There is no evidence either driver had exceeded the speed limit, nor had Watfa caused or contributed to the crash.

One of two central questions for the jury is whether Watfa was carrying the unrestrained baby on his lap, substantially contributing to his death.

The other question is if the manner of driving lowered the standard of care so it involved a high risk of death.

Following the Crown's official opening due on Wednesday, the jury will hear from witnesses including several Lurnea residents, and a number of experts and forensic pathologists.

Australian Associated Press