The mother of the three Abdallah children says she has forgiven the alleged drunk driver who killed her three children in Sydney's north-west.

Just before 8pm on Saturday, Anthony, Angelina and Sienna Abdallah were walking with four other children along a footpath on Bettington Road, Oatlands, when police allege Samuel Davidson's Mitsubishi Triton mounted the kerb and hit the group.

The three siblings and their cousin, Veronique Sakr, were killed instantly, while the other children were taken to hospital.

On Monday, their mother Leila returned to the scene that has become a makeshift memorial, flooded with hundreds of flowers, rosary beads, teddy bears and other tributes.