The boy who died after an accident at Beamish Open Air Museum has been named as Karl Doran.
Karl, seven, died after an incident with steam traction engine and a trailer.
The engine was being driven by Karl's father Phillip, 41.
Karl lived with his parents in Darlington.
A post mortem examination carried out last night showed that he died from head injuries.
DCI Victoria Fuller, who is leading the investigation, said: "We are treating this as a tragic incident and are working with our colleagues at 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 tran which passed the traction engine around the time of the incident which occurred at around 3pm [on Sunday July 22]."
Karl and his father were both steam enthusiasts and were frequent volunteers at Beamish.
Richard Evans, museum director, said: "We continue to support the joint investigation and offer our deep condolences to Karl's father."
Beamish Museum is opening despite the incident in which a child died. The museum closed immediately after it happened on Sunday afternoon but said it would disappoint visitors if it did not open again today.
The safety of our visitors and staff is our top priority. The decision to open today was taken after consultation with Durham Police and the Health and Safety Executive.
This tragic accident involved a steam roller and all road steam has been suspended until completion of the investigation.
The Museum is aware of many people planning to travel a long distance to visit today and felt it should open so as not to disappoint these people.
Our thoughts remain with the family, and we thank everyone for their kind words.
A visitor has described how paramedics desperately tried to bring the boy back to life.
Cllr Carl Marshall said: "I was visiting the museum with the family. We were in the events field. We noticed an incident."
"There was what appeared to be a child. There were Beamish vehicles on scene. The paramedic arrived and started to work on the casualty. Within a couple of minutes things got more frantic. A defibrillator came out."
"The after a couple more minutes they walked away and a blanket came out."
"It's a tragic event and it has rocked this community."
A seven-year-old boy was killed in the incident with a steam traction engine and trailer at the Beamish Museum.Read the full story ›
Durham Police have confirmed that a young child has been killed in a tragic accident at Beamish Museum in County Durham.
Emergency services are at the scene and the park has been evacuated.
There are reports that the child was a young boy.
Croquet, ping pong and 'sheaf tossing' were the main events at an Edwardian sports day at the Beamish Museum.Read the full story ›
A draw has been made to select who will have the honour of collecting a splinter of the English Flame and bring it to a ceremony in the North East.
The Flame Celebration is being held at the Beamish Museum in County Durham on August 24.
Part of the English Flame (which will later become the Paralympic Flame) is being brought up from Trafalgar Square in London by a nominated disabled person. The flame will then be used at the ceremony in Beamish.
Former Paralympic athlete, Baroness Tanni Grey Thompson made the draw at The King's Academy in Middlesbrough this afternoon.
The winning nominated will be announced on June 8.