A five-year-old girl cried out for her mother moments before being fatally struck by a car in Sydney's west, a jury has heard.

Taylor Maddock and her daughter Alannah Sobolewski were on a pedestrian crossing on Rooty Hill Road North in Plumpton after picking up pizzas from Domino's when they were hit at 7.15pm on March 17, 2021.

Alannah was rushed to Westmead Hospital, but died later that evening, after being struck by a Toyota Tarago van driven by Abel Elias Lopez.

Ms Maddock, 27, also received significant injuries to her leg, hip and back, requiring surgery and multiple hospital visits over the past two years.

As a trial against Lopez in the Parramatta District Court started on Monday, she entered the courtroom using a walking frame and described how she was holding her daughter's hand when she assumed it was safe to cross the road.

"(Alannah) yelled, 'Mum!' and I turned and that was it. That was it. All I heard was, 'Mum!'," she told the jury.

"It was just 'bang' straight away. I remember rolling up on the windshield and then rolling all the way back down."

Lopez stared at the ground during Ms Maddock's emotional testimony. He has pleaded not guilty to two charges of dangerous driving occasioning death and grievous bodily harm.

Defence barrister Slade Howell said his client had slowed down before the crossing but the rain, glare from oncoming traffic and inoperative flood lights above the crossing meant he did not see the mother or her child.

The clothing worn by the victims, including a black umbrella, the colour of the background and other visual distractions were also to blame, the jury heard.

"From his perspective, the impact happened quickly and they came from nowhere," Mr Howell said.

While Ms Maddock told police she had seen Lopez and his vehicle slow down before the impact, she explained to the jury that this was only a belief of what drivers typically did when they approached a zebra crossing

Earlier on Monday, crown prosecutor Louie Christoff said while it was dusk and sprinkling rain at the time of the collision, street lights along the road were illuminated and vehicles were using their headlights.

Witness Aaron Wilson, who was driving behind Lopez, is expected to give evidence that he was travelling at the speed limit of 60 km/h and only saw the Tarago's brake lights come on after it hit Ms Maddock and her daughter.

Speaking with police at the scene soon after the incident, Lopez claimed he was already driving below the speed limit and was in no rush to get home.

He said he slowed down in anticipation of the upcoming crossing.

Mr Christoff said Lopez was driving dangerously because he did not decrease his speed before the crossing and failed to keep an adequate lookout for pedestrians.

"Those matters in particular give the accused's driving the quality of dangerousness," he said.

The trial before Judge Andrew Colefax continues on Tuesday.