"She'd had a brilliant year," her grandmother said.

But tragedy struck at 9.20am on Wednesday when a white Nissan Dualis was involved in a collision with Zoe, 5, her sister Elle, 4, their cousin Akshay, 6, and Akshay's 38-year-old mother as they crossed a driveway into the school.

Akshay and Elle were pinned under the car, killing Akshay instantly and breaking Elle's pelvis in two places.

The stretch of road outside Carlingford Public School was considered so dangerous during drop-off hours that the Department of Education had issued a directive banning parents from using the school's driveways, the local council had started sending infringement officers to fine drivers and principal Neil Hinton had repeatedly begged parents to be more careful.

In March, a group of students was almost hit by a distracted parent who was ''oblivious to the fact that … one of our teachers was escorting a number of students across the crossing'', Mr Hinton wrote to parents. ''Unfortunately, there are still a number of parents who are disobeying road rules and jeopardising our students' safety when dropping their children to and from school.''

Parents screamed in horror as a 46-year-old Carlingford mother, with her two Carlingford Public School students on the back seat of her car, ploughed across the footpath and driveway on Rickard Street, crashing into a fence and pinning Elle and Akshay under the car.

She was treated for shock and still had not been interviewed by police on Wednesday evening.

Zoe's kindergarten teacher was by her side as she was taken to hospital and later discharged with minor injuries. Her aunt sustained a knee injury.

Akshay was visiting Sydney from Malaysia with his mother and had been in the country for just a week, staying with Zoe, Elle and their parents Andrew Stephen and Fung Lui Ong in Carlingford.

Ms Fung's 38-year-old sister was walking Zoe to school and had taken Elle and Akshay with her.

Kindergarten student Joyslyn Shin, 6, cried as she said she planned to go to Macquarie cinema with her best friend Zoe and Akshay on Friday afternoon. ''It's sad,'' Joyslyn said, gripping onto her mother's hand.

Police Superintendent John Duncan said it was too early to determine the cause of the ''freakish'' and ''traumatic'' accident. ''This is a tragic incident indeed,'' he said. ''It's a week before Christmas and the last day of school.''

Mr Hinton said he would ''consult police after their investigation is complete to determine if there is anything further the school can do to improve pedestrian safety in and around its grounds''.

In September, he told parents they were prohibited from driving into school grounds to drop off or collect children. ''This is a directive from DEC and is in place to ensure the safety of our students,'' he wrote in a newsletter.

with Megan Levy