Jessica West, 37, and her five-year-old son Deighton were killed when truck driver Michael Brent Knowler failed to give way at an intersection and hit the family's Rav4, causing it to flip, on December 29, 2019.

Knowler, 60, was driving a Kenworth prime mover on Church Parade towards his friend's home in Broomfield before the fatal collision occurred.

He appeared via a video link from prison at the County Court of Victoria on Wednesday for a further plea hearing.

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The prosecution asked the court for an adjournment for the police informant and investigators to look at an engineer's report of the road where the collision occurred.

The hearing was adjourned for a second further plea hearing on May 10 and Knowler was remanded in custody.

A date for Judge George Georgiou to sentence Knowler was not arranged on Wednesday.

At a further plea hearing, the prosecution and the defence will present additional information they want the judge to take into account when deciding on the sentence.

A sentencing hearing is usually held on a separate day.

Knowler pleaded guilty in the County Court in February to two counts of dangerous driving causing death and one count of dangerous driving causing serious injury.

The court was told Knowler was using a GPS on his phone because he was unfamiliar with the area and he told police he checked his mobile phone after seeing a sign indicating there was an intersection ahead.

Knowler admitted to police he was "probably travelling too fast" when he first saw the give way sign and did not realise until the point he had to stop.

He said he was unable to see the Rav4 approaching because of the trees on the right hand side of the road until he was entering the intersection and put the brakes on.

Knowler hit the passenger side of the West family's car, pushing it across the intersection, causing it hit a roadside culvert and flip between three and five times before coming to rest on its roof.

The West family with the family dog in the back had been travelling from their home in Epsom near Bendigo to Mrs West's parents' house in Ballarat.

Mr West was driving the family car, with Mrs West in the passenger seat and their two children Oakley, 9, and Deighton, 5, in booster seats in the back.

Mrs West and Deighton were declared dead at the scene.

Mr West was taken to Ballarat Base Hospital with minor injuries and Oakley was transported by air ambulance to the Royal Children's Hospital with serious injuries.

The family dog was killed.

The court was previously told Knowler was an experienced driver, had driven more than 11,000 kilometres in the same truck and had no driving or criminal record.

Judge George Georgiou is presiding over the case.

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