A drunk driver slammed his pickup truck into a group of children in Sydney, killing two sisters, their brother and a cousin and seriously injuring three others, police alleged on Sunday.

The 29-year-old driver was charged with manslaughter and high-range drink driving following the incident late Saturday in the Oatlands suburb of western Sydney.

The children were on a footpath when the four-wheel drive jumped the curb and rammed into them, police alleged.

Three girls aged 8 to 12 and a 13-year-old boy died at the scene and two other girls and a boy were injured and taken to hospital, where they were in a stable condition Sunday, police said.  

The dead included two sisters and their brother, three of the six children of Daniel and Leila Abdallah.

"Yesterday I lost three of my children. I had a cousin, Bridget, she lost her daughter as well," Daniel Abdallah told reporters Sunday morning.

"I'm numb, probably that's how I feel at the moment," 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."

The driver, whose name has not been released, was due in court Sunday facing 20 charges.