An air ambulance landed in Sandall Park after the collision in nearby Barnby Dun Road at about 5.50pm on Saturday.
A South Yorkshire Police spokesman said: "The seven-year-old suffered serious injuries in the collision and was taken to hospital to receive treatment.
"The road was closed at the time of the incident but later reopened."
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The girl's current condition is unknown. Police have not revealed any more details of the incident.