The parents of a man charged with the manslaughter of four Sydney children in an alleged drunk driving incident say they are devastated over the tragedy.

Retired police detective Allan Davidson and his wife Kay on Monday said they have been left shattered by the incident, just days after their son Samuel, 29, allegedly drove into the group of children in Oatlands as they walked to buy ice creams.

Antony Abdallah, 13, and his sisters Angelina, 12 and Sienna, 9, were killed, along with their cousin Veronique Sakr, 11.

“Those poor families have lost their children and no words can help them. And I am so sorry for them,” Mr Davidson told Nine News.

Speaking of his son, Mr Davidson said, “He is so, so sorry … He has a good heart and I am sure he is devastated just as we are.”

He said the couple was no stranger to grief after losing their daughter 10 years ago and “now effectively we’ve lost our son”.

The grief-stricken mother of three of the dead children on Monday said she won’t hate the man who was behind the wheel.

Leila Geagea, the mother of Sienna, Angelina and Antony, said she forgave Davidson as she visited the scene of the tragedy on Monday.

“I think in my heart I forgive him. But I want the court to be fair. I’m not going to hate him because that’s not who we are,” she told reporters.

Hundreds of people gathered at the Oatlands crash site on Monday night to lay flowers and show support for the grieving families, according to media reports.

The fatal crash has sparked a renewed push for a road rules overhaul in NSW.

-with AAP