A seven-year-old boy who died at an open-air museum was crushed to death by a steam engine driven by his father.
Karl Doran, of Darlington, died in what police described as a "tragic accident" on Sunday afternoon.
He and his father Phillip, 41, were at a steam rally at Beamish museum in County Durham.
Karl suffered major head injuries after he was hit by the steam traction engine and trailer, which was being driven along a road adjacent to the railway line in the museum.
Durham Police said: "A post-mortem examination carried out last night (Sunday) showed that death was due to a head injury. We can also confirm today that the steam traction engine was being driven by Karl's father, 41-year-old Phillip Doran.
"Mr Doran was taken to hospital suffering from shock immediately after the incident but has since been able to speak to police."
Detective Chief Inspector Victoria Fuller, who is leading the joint investigation, said: "We are treating this as a tragic incident and are working with our colleagues in the Health and Safety Executive to establish the exact circumstances.
"We have already spoken to a number of witnesses but need to speak to some key people who may have been on a bus or tram which passed the traction engine around the time of the incident, which occurred at around 3pm."
Karl and his father, both steam enthusiasts, were frequent volunteers at Beamish.
Richard Evans, the museum's director, said: "We continue to support the joint investigation and offer our deep condolences to Karl's family."