A 16-year-old boy arrested on suspicion of causing death by dangerous driving after a collision on the Shirenewton caravan site, east of Cardiff, has been released on bail pending further enquiries.
A seven-year-old boy was taken to the University Hospital of Wales in Cardiff, where he died from his injuries. Specially-trained police officers are supporting the family.
Police are still investigating the incident, which happened at around 3pm on Saturday. They are appealing for any witnesses to come forward.