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
ComRes polling agency chairman says the next 100 days will be be gruelling in the most uncertain General Election that anyone can remember.
David Cameron has pledged to reduce the annual benefits cap to £23,000 "within the first few days" of a Conservative election win.
Damp and murky over hills. Mostly dry.