The father of three of the four children killed in a horror crash at Oatlands near Parramatta has spoken of his devastating loss the morning after the tragedy.

Key points: Four children have been killed and three are in hospital after a pedestrian crash involving a 4WD

Four children have been killed and three are in hospital after a pedestrian crash involving a 4WD Emergency services attended the scene at Oatlands near Parramatta just before 8:00pm on Saturday

Emergency services attended the scene at Oatlands near Parramatta just before 8:00pm on Saturday Police said the 4WD driver returned a positive result to a roadside breath test

Daniel Abdallah and his wife Leila lost three of their six children on Saturday night.

Just before 8:00pm, emergency services were called to Bettington Road near the Oatlands Golf Club, where seven children had been hit by a 4WD allegedly driven by Samuel Davidson, 29.

Mr Abdallah's children Antony, 13, Angelina, 12 and Sienna, 9, were killed in the crash.

His cousin Bridget lost her 11-year-old daughter, Veronique Sakr.

Angelina, 12, Sienna, 8, Antony, 13, and Veronique, 11 were all killed in the incident. ( Supplied )

"I don't know what to say, I'm numb," he said.

"All I just want to say is 'Please, drivers be careful'. These kids were just walking innocently, enjoying each other's company, and this morning I woke up — I have lost three kids."

Mr Davidson has been charged with 20 offences including four counts of manslaughter, four counts of dangerous driving occasioning death from driving under influence, four counts of dangerous driving occasioning death, driving with a high-range blood alcohol reading and driving through a red light.

The three children's mother, Leila (right), at the crash site on Sunday. ( AAP: Joel Carrett )

At Castle Hill Police Station, he allegedly returned a reading of 0.150, three times the legal limit.

Davidson's case was heard at Parramatta Bail Court on Sunday. Mr Davidson did not appear and there was no application for bail.

The case has been adjourned until April 2 at Parramatta Local Court.

Mr Davidson and a 24-year-old male passenger were both uninjured in the crash.

Police said the passenger had tried to assist at the crash scene.

Three of the children killed were girls and the other was a boy. ( ABC News )

Father says children have 'gone to a better place'

Mr Abdallah described his son Antony as a "very handsome boy" who loved basketball.

"Actually he woke up that morning and said, 'We're going to play this game for Kobe [Bryant]'."

He said Angelina was "my little helper … anything I needed, she had my back."

Sienna, he said, was "my little diva, little actress".

"They have gone to a better place," he said.

Leila and Daniel Abdallah lost three of their children in the crash. ( Supplied )

He said all the children involved were related and the cousins had come over to the Abdallah house.

"They were all coming over to get babysat. I told them, 'Just go for a walk, little walk, stay together. You should be OK'," he said.

"Give a little bit of independence, you know, and this is one-in-a-million.

"They didn't do anything wrong. They were just walking on the footpath.

"Please just make sure you love your loved ones, your kids especially."

Bystanders and emergency services at the scene last night. ( ABC News )

Veronique was in Year 6 at Santa Sabina College in Strathfield.

The school said students would be notified about a memorial for Veronique this week.

Three other children, an 11-year-old boy and two girls aged 10 and 13, were treated at the scene by NSW Ambulance paramedics before being taken to the Children's Hospital at Westmead.

One boy was thought to be in a critical condition, but is now stable and two girls were treated for non-life-threatening injuries.

Acting superintendent for Police NSW Danielle Emerton said the families of the children were front of mind.

"This is about the families … they have lost four children and three are in hospital and it must be devastating for them," she said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 42 seconds 42 s Four children killed after being hit by 4WD

'A difficult, horrific scene'

Speaking at Castle Hill Police Station on Sunday, an emotional Assistant Commissioner Michael Corby from the Traffic and Highway Patrol Command spoke about the "absolutely tragic event".

"Our thoughts go out to the families concerned. Because all of the children were related, it makes it all the more tragic for the families," he said.

He said emergency services, assisted by a number of local people, had attended "a difficult scene, it was very horrific".

"Nothing could be done for the four children that died," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 13 seconds 3 m 13 s Assistant Commissioner Michael Corby says it is hard to imagine the grief the family is currently experiencing.

Assistant Commissioner Corby said there were several witnesses and police had a "very strong case", and would be prosecuting the charges to the fullest extent of the law.

He reiterated that drink-driving and speeding would not be tolerated.

"Tragedies do occur, but in my time in policing, this is one of the most tragic, involving young children dying in a very tragic circumstance," he said.

"It is hard to imagine the grief that the family is going through at the moment."

'Chaos and carnage'

Eighteen paramedics attended the scene on the suburban road.

Acting superintendent NSW Ambulance Andrew McAlpine said the scenes were confronting.

"This is incredibly hard for all the emergency services, notwithstanding the loss the families have sustained," he said.

"It's very difficult for police, for paramedics, for fire and rescue to be confronted with such chaos and such carnage."

Police have begun an investigation into the crash, the scene of which will be examined by specialist police from the Metropolitan Crash Investigation Unit.