The family’s Mitsubishi Pajero slammed into a tree just after 9.30am on Sunday near the wheatbelt town of Williams.
The impact caused the vehicle’s bull bar to wrap around the tree’s trunk.
An eight-year-old boy, his 10-year-old sister and their parents were all injured in the crash but managed to survive.
At least one of the occupants was trapped in the wreck, forcing emergency services to pry the car’s doors open to free them.
Both children were airlifted to the closest hospital, in Narrogin, while their parents were flown by two rescue helicopters to Royal Perth Hospital.
It is unclear what caused the single-vehicle crash or if the wet weather was a contributing factor.
Major crash unit detectives are investigating.
This content first appear on 9news