STORY: Detectives said the girl had been taken to hospital and remained in a life-threatening condition after the shooting not far from Euston train station in north London.
A 12-year-old girl was also among those injured and had been taken to hospital with a minor leg injury but later discharged.
"Any shooting incident is unacceptable, but for multiple people, including two children, to be injured in a shooting in the middle of a Saturday afternoon is shocking," Superintendent Ed Wells said in a statement.
"An investigation into this dreadful attack is already well under way involving local officers and specialist detectives."
Police said four women, aged 21, 48, 54 and 41, were also taken to hospital after the shooting, with the 48-year-old said to have suffered potentially life-changing injuries.
"The incident took place in the vicinity of a church where a funeral was taking place," a police statement said. "Initial enquiries suggest the shots were fired from a moving vehicle which was then driven away from the scene."