A second child has died following a collision in Truganina on Saturday.
A 10-year-old girl died at the scene, after a Ford Territory travelling along Hopkins Road overtook a Honda SUV and collided head-on with a Ford Focus about midnight.
The Territory then also collided with the Honda SUV.
A man and woman with two children, including the girl who died, were travelling in the Ford Focus.
A four-year-old boy from that vehicle has died in hospital this evening.
The female driver remains in a critical condition while the male passenger has been released from hospital.
The 41-year-old male driver from Rockbank, and sole occupant of the Ford Territory, was taken to hospital with non-life threatening injuries.
Five occupants in the Honda SUV were not injured.
Major Collision Investigation Unit detectives are investigating and the driver of the Ford Territory remains in hospital and is yet to be interviewed.
Anyone who witnessed the collision is urged to contact Crime Stoppers on 1800 333 000.