Police have named the 11-year-old boy who died after being hit by a tractor at a farm in Rothwell as Harry Whitlam, from the Wakefield area.
The tractor driver a, 48-year-old local man, was arrested on suspicion of drink driving and causing death by dangerous driving.
Detective Superintendent Scott Wood, of West Yorkshire Police, said: "We are continuing to investigate what has been a tragic incident with the Health and Safety Executive and are still appealing for witnesses to what occurred yesterday.
"Anyone who witnessed the incident is asked to contact West Yorkshire Police Major Collision Enquiry Team on 01924 293047 or via 101."
More top news
Pregnant women who go to sleep on their back during the later stages of pregnancy face an increased chance of a stillbirth, a study found.
Historic mills across the North are disappearing fast despite massive public support against demolition, Historic England has claimed.
Barnsley singer Holly Tandy has been voted out of this year's X Factor. She was one of the two acts with the fewest votes on Sunday night.