Mother and children hit in Sydney car park

A seven-year-old girl has suffered serious head and leg injuries after a car struck her and her mother and three year old sibling in a fast food car park in Sydney's west.

Police say a car exiting the drive-through at the restaurant on Hassall Street, Rosehill struck the family as they walked through the car park about 8.30pm on Sunday.

The 37-year-old woman and three-year-old child were uninjured, but the seven-year-old girl received serious injuries and was taken by ambulance to Westmead Children's Hospital where she is in a critical but stable condition.

Police have appealed for witnesses to contact Crime Stoppers on 1800 333 000.