Harry Whitlam, 11, was airlifted to hospital and underwent complex emergency surgery yesterday afternoon after being knocked down at Swithens Farm in Rothwell, near Leeds, hours earlier.
He died last night.
It is believed Harry, who came from the local area, was working as a farm hand at the facility, where his mother is also understood to work.
He is thought to have suffered head injuries after being hit by the tractor’s trailer at 9.20am.
He was later flown by Yorkshire Air Ambulance to Leeds General Infirmary.
The vehicle is understood to have been reversing at the time of the collision.
A West Yorkshire Police spokesman said: “At about 9.20am on Friday, police were contacted by the ambulance service who were attending Swithens Farm, in Swithens Lane, Rothwell, where an 11-year-old boy had been injured in a collision with a tractor.
“He was taken to Leeds General Infirmary by air ambulance for treatment.
“A 48-year-old local man has been arrested on suspicion of drink driving.”
A Yorkshire Air Ambulance spokeswoman said following the accident: “We were called at 9.15am to an incident in Rothwell, where a boy has suffered life-threatening injuries.”
She added that a doctor was on board the air ambulance yesterday, providing additional medical support to the paramedics.
No one from the farm, which remained open to visitors after the incident, was willing to comment yesterday.
However, Elmet and Rothwell MP Alec Shelbrooke expressed his shock at what had happened.
“It’s a tragic incident and my immediate thoughts go out to his family, especially if they have links to the farm,” he said.
He added: “The investigation should now be allowed to take its course.”
The farm, which is run by Ian and Angela Broadhead, has a shop, playground, play barn and open farm.
The incident happened on a dirt track next to two of the farm’s barns.
Police were at the scene for much of the day speaking to farm employees and gathering evidence.
Joanna Baron, who was at the farm with her son Elliott, four, said: “I can’t believe it, it’s awful.
“We come here a lot and it’s such a lovely place to be.
“It’s shocking, ” she added.
Emma Clough, who was visiting with her children Mia and Jack, said: “I just feel for the family.
“What they’re going through is unimaginable.”
Detective Superintendent Scott Wood said: “We have specialist collision investigators working with the Health and Safety Executive to establish what happened.
The Health and Safety Executive confirmed it was supporting the police investigation but was unlikely to carry out any separate inquiries of its own.
The farm’s website describes it as an educational facility designed to show children how working farms operate.
It says: “By opening the doors of Swithens Farm, they hope to offer the fantastic experience of farm life to others, teaching kids how the food they eat ends up on their plates.
“‘From field to fork’, visitors can be part of the food journey, feeding and petting the animals, and then eating and buying the final products.
“All of the food sold at Swithens is either produced from the farm’s animals or sourced from other farms and outlets in the area, causing minimal impact to the environment and supporting other local businesses.”
Witnesses to the incident should contact West Yorkshire Police’s major collision enquiry team on 01924 293047 or by calling the non-emergency number 101.