A drunk and drugged driver who killed four children in a crash at Oatlands, in Sydney's west, has been sentenced to only 28 years in prison.

Samuel William Davidson crashed his ute while excessively speeding, mounted a curb, and hit a group of seven children in February last year.

Siblings Antony, 13, Angelina, 12, and Sienna Abdallah, 9, and their cousin, Veronique Sakr, 11, died at the scene.

Three other children were injured in the crash, one of them has been left with a permanent brain injury.

Judge James Bennett described Davidson's driving as "menacing" and a "horrific example" of misconduct.

"Tragedy was inevitable," Judge Bennett said.

"The magnitude of the tragedy, though, unimaginable.

Davidson, 30, pleaded guilty to several charges, including four counts of manslaughter.

On the day of the crash, he had spent more than 12 hours drinking, and he was three times over the legal limit when he hit the children, he also had cocaine and other drugs in his system.

The court heard that immediately after the crash Davidson, who was uninjured, said: "What have I done? I've killed people. I'm going to jail." 

Judge Bennett sentenced Davidson to a "substantial" jail term of 28 years.

He will be eligible for parole in 2041.

The court heard witnesses saw Davidson, in the lead-up to the crash, excessively speeding, driving on the wrong side of the road and running red lights.

The ute continued for 90 metres after hitting the children.

Judge Bennett described the behaviour as "menacing driving".

Emotional family members of the victims filled the courtroom. Some left while injury details were read out.

Davidson wiped away tears at times during the hearing and had the judge read out a letter of apology to the victims' families.

"I am so sorry for what happened and what I did to your wonderful family," it said.

Video and images from the night of the crash show chaos and carnage at the scene, as people and bystanders in the suburban area rushed to help.

The deaths saw a huge outpouring of grief in the community, with hundreds attending funerals and vigils.

A makeshift shrine at the site was created the next day, where family members of the children attended to pray.

"These kids were just walking innocently enjoying each other's company, and this morning I've woke up, I've lost three kids," father Daniel Abdallah said at the scene.

Video from the night shows a shirtless and handcuffed Davidson being led away by police.

At a pre-sentencing hearing last month, the mother of three of the children said she was no longer the same person.

"You have killed us all, I am no longer living — just existing," Leila Abdallah said.

Veronique Sakr's father, Bob, called on the judge to hand down the "most extreme sentence".

"The only time a father should walk his princess down a church aisle is for her wedding ... instead I carried her down the aisle for her funeral," he said.

Story By | Jonathan Hair