The crash occurred near the intersection of Nerowie and Parwan-Exford roads in Parwan just before 4pm on Tuesday. According to Victoria Police, a 4WD carrying seven children rolled, killing a seven-year-old girl at the scene. An 11-year-old boy was flown to hospital in a critical condition but died overnight.
Five other children were taken to hospital with non-life-threatening injuries. The driver, a 34-year-old woman, was taken to hospital for observation.
Detective Sergeant Tony Gentile from the Major Collision Investigation Unit said the woman had picked the children up from school. "From my understanding, the scene was quite hectic, people everywhere, witnesses who witnessed it, they stopped and rendered assistance," he said.
"Obviously, with seven children, they were distressed and they were cared for by paramedics, members of the public and police."
Gentile described the incident as a "really sad set of circumstances" and urged the public to "drive to the conditions and be mindful of their surrounds".
Police have asked anyone who witnessed the crash or has dash cam footage to come forward.