The boy was pronounced dead at 4.35pm after being taken for treatment at a south London hospital following the collision. His family have been informed and are being supported by specialist police officers.
Two other pedestrians, a 40-year-old woman and an eight-year-old boy, suffered injuries and were taken to hospital. Their injuries are not thought to be life-threatening.
The 40-year-old van driver stopped at the scene and was arrested on suspicion of causing death by dangerous driving, and taken to a south London police station. He was later released under investigation.
Officers from the Roads and Transport Policing Command are investigating.
Detective Inspector Lucie Card, leading the investigation, said: “This is a tragic incident which has resulted in the death of a 14-year-old boy.
“Our investigation into what happened is well under way but we need anyone who witnessed what happened to come forward and speak to us.
“Likewise, I would also ask any motorists in the area to review any dashcam footage that may have captured this collision.
“It is vital that with give this child’s family answers about what led to his death just a few days before Christmas.”