Four children have been killed after being struck by an alleged out-of-control 4WD. The driver tested positive in a breath test.

Police say the man allegedly behind the wheel of a ute that mowed down and killed four children in western Sydney this weekend was driving on the wrong side of road and ran a red light before the crash.

Samuel William Davidson, a builder, was allegedly three times over the legal blood alcohol limit on Saturday night when his Mitsubishi ute mounted a kerb in Oatlands and struck seven children on the footpath.

The children were believed to be going for ice cream when they were walking along Bettington Road in Oatlands, near Parramatta, about 8pm that night.

Siblings Antony Abdallah, 13, Angelina Abdallah, 12, Sienna Abdallah, eight, and their 11-year-old cousin Veronique Sakr were killed.

Three others were seriously injured, including an 11-year-old boy and two girls, aged 10 and 13, who were taken to The Children’s Hospital at Westmead. The boy remains in a serious but stable condition and both girls are stable.

Police allege the driver, 29, had been drinking at home with friends before he got behind the wheel to withdraw cash at a service station, less than 2km away.

The Daily Telegraph reports that Davidson and a 24-year-old friend were returning home when the 29-year-old is alleged to have gone through a red light and was seen travelling on the wrong side of the road just seconds before he allegedly killed the children.

One female driver said she witnessed the car careening towards the direction of pedestrians and honked her horn to alert the driver.

Davidson was arrested at the scene and remains in custody. He was seen being taken away in handcuffs and shirtless.

Police say he was uninjured, given a breath-test following the incident and returned a reading of 0.150, three times above the legal limit.

He has been charged with 20 offences including four counts of manslaughter, dangerous driving occasioning death and grievous bodily harm, negligent driving and drink-driving.

Davidson’s case was heard on Sunday at the Parramatta Bail Court, according to AAP, but he did not appear and did not apply for bail, which was formally refused by magistrate John McIntosh.

He’s scheduled to return to Parramatta Local Court on April 2.

AAP reported that Mr McIntosh visibly shook his head while reading the facts of the case. Three of the children killed in Saturday’s incident were siblings from the Abdallah family and the fourth was their cousin.

Danny Abdallah, the father of the victims aged 8, 12 and 13, told reporters on Sunday he and wife Leila were heartbroken. They both visited the site on Bettington Road on Sunday morning, with Leila extremely distressed.

Distraught members of the Oatlands community on Sunday also placed flowers at the scene, with shrines established for each of the Abdallah children.

“I don’t know what to say. I’m numb, probably that’s what I feel at the moment. All I want to say is please, drivers, be careful,” Mr Abdallah said. “These kids were just walking innocently, enjoying each other’s company ... and this morning I woke up and I have lost three kids.” The seriously injured child was not from the Abdallah family.

He was taken to The Children’s Hospital in Westmead in a critical condition but is now in a serious but stable condition.

NSW Ambulance Acting Superintendent Andrew McAlpine on Saturday evening said paramedics had attended a horrific scene.

“This is incredibly hard for the emergency services, notwithstanding the losses that the families have sustained,” he told reporters.

“It’s very, very difficult for police, for fire rescue, for paramedics to be confronted with such chaos and carnage.”

NSW Police Assistant Commissioner Michael Corboy told reporters on Sunday the driver was charged after refusing to be interviewed by police but they were speaking with witnesses.

“Tragedies do occur but in my time in policing, this is one of the most tragic involving young children dying,” Mr Corboy said.

Acting Assistant Commissioner Jason Joyce said the driver remained at the scene until the police arrived and there were indications his 24-year-old male passenger tried to help some of the children.

Mr McAlpine said approximately 18 paramedics and a number of doctors attended after receiving reports of “a number of pedestrians hit by a vehicle”.

“When the first crews arrived on scene they were confronted with carnage,” he said.

“Very, very difficult scene with obviously a lot of chaos. It’s incredibly hard for all the emergency services, notwithstanding the loss the families have sustained.

“It’s very, very difficult for police, fire rescue, paramedics to be confronted with such chaos and such carnage.”

- With AAP