Emergency services rushed to Tooting Bec Road, in Lambeth, on December 12 after reports an 11-year-old girl had been hit by a car.
London Ambulance Service crews treated the girl for her injuries, before taking her to hospital, but she later passed away on January 5.
A 54-year-old man was arrested at the scene on suspicion of causing injury by dangerous driving and on suspicion of driving under of the influence.
He has since been bailed while enquiries continue.
The Metropolitan Police is appealing for anyone with information on the incident to get in touch.
Detective Chief Superintendent Emma Bond, who leads policing in the area, said: “The victim’s family are going through unimaginable pain, and our thoughts remain with them at this time.
“We have spoken to a number of people who witnessed the collision, but we would like to encourage anyone else who was in the area at the time of the incident to come forward with any information that may assist the investigation.”
The crash happened at the junction of Garrads Road and Tooting Bec Road.
Anyone with information is urged to call 101, quoting reference 3570/12DEC25.
