A baby girl has died two days after she was pulled from the wreckage of a car crash in Sydney’s southwest that killed her mother and brother.

NSW Police said the three-month-old, named in media reports as Ivy Prahastono, died in the Children’s Hospital Westmead Hospital on Wednesday morning.

Her 34-year-old mother Katrina Prahastono was driving a Mazda SUV on Monday morning when it was involved in a crash with a cement truck.

Ms Prahastono and her two year-old-son Kai died at the scene, while critically injured Ivy was rushed to hospital.

The 48-year-old truck driver was not injured.

Police are investigating the crash and have urged anyone with dashcam vision in the area at the time or anyone with further information to come forward.