In a statement, the Brititish Transport Police said:
"A four-year-old girl, Emma Lifsey, sustained serious injuries and was airlifted to Sheffield Children's Hospital, where she was sadly pronounced dead in the early hours Wednesday, 5 December. Her family have been notified.
"The police investigation into the incident is ongoing and remains very much in the early stages. Officers are working hard to establish the full circumstances surrounding the incident, including how the vehicle came to be on the tracks at the time."
More top news
Once a year W11 comes alive with the colour of carnival. Everything you need to know about getting around and what to see in Notting Hill.
People should only be allowed to move freely within the EU if they have a job waiting for them, the Home Secretary has said.
A 62-year-old woman has been found alive more than a week after she vanished while on a hiking trip.