BBC North of England Correspondent John Thorne reports from Sheffield

A post-mortem examination will be carried out on the body of Usman Ali, who was taken to Sheffield Children's Hospital after falling during supervised activities at lunchtimeon Wednesday, 18 November.

A statement from the school said: "He showed no adverse reaction during Wednesday afternoon and enjoyed himself at a children's party in the afternoon. Tragically the boy died at the weekend.

"As in all cases of unexpected deaths there will be an inquest, no-one knows the cause of death at this stage.

"The school is shocked and saddened at the child's death and all thoughts are with the boy's family and relatives."

The hospital's Chief Nurse Hussein Khatib said a formal investigation was "a matter of procedure" if a child is returned to casualty within 24 hours of an initial treatment.

"We sympathise with the family, who obviously had a heartbreaking decision to make, and we will share the findings of the inquiry with them," he said.

'Very traumatic'

The boy was treated in the hospital's casualty department and sent home after a playground accident at the local authority-run Mossbrook School for children with special needs in Sheffield.

Hours later, he was admitted for emergency surgery after his parents became alarmed by his worsening condition.

But the operation failed and his life support machine was switched off on Sunday when it became clear that he stood no chance of recovery.

Sheffield Director of Education Jonathan Crossley-Holland said counselling and support would be offered to children and teachers.

"The death of a young child is always very traumatic, but I think the shock is even greater when it involves a small, close-knit special needs school," he said.

South Yorkshire Police have been conducting interviews of staff and parents in an attempt to ascertain how the accident happened, but no conclusion has yet been reached.