An inquest heard a report into Jack Sands' death at Leeds General Infirmary concluded that antibiotics "could have and should have" been given to him more than three-and-a-half-hours earlier than they were.
A nurse told the inquest that sepsis "wasn't on the radar" on the ward Jack was being treated on the time of the tragedy in July 2018, but that staff had since received sepsis training.
Jack had a bacterial infection on the surface of his brain died five days after an operation in July 2018 to reshape his skull.
The inquest heard the operation - to avoid him having an abnormally shaped head - had only around a one per cent chance of going badly wrong.
Jack had been suffering from vomiting and diarrhoea and had mottled skin following the operation.
His parents Gemma and John Sands of Hook near Goole had raised concerns about his treatment as a dozen doctors dealt with him over the weekend.
The operation on Thursday July 12 2018 went to plan and Jack was due to be allowed home on Saturday July 14, but he started suffering from sickness and diaorrhoea that afternoon.
He was diagnosed with gastroenteritis and and treated with fluids.
Senior ward sister Julie Cooper told the inquest she came on duty on the morning of Monday July 16 and was concerned that Jack was lethargic and had a slower than normal heart rate.
Nurse Cooper said at around 7pm on Monday she asked for an emergency crash call to be put out for doctors to immediately review Jack.
The inquest heard Dr Jonathan Chan noted Jack's skin was mottled and he suspected he was suffering from viral gastroenteritis.
Dr Demetria Demetriou examined Jack at 9.30pm on Monday and diagnosed Jack with either sepsis or dehydration.
The inquest was told Jack was started on antibiotics at 11.30pm that night.
Jack's condition worsened and he was taken to the intensive care unit, where he suffered two cardiac arrests.
His death was confirmed just after 4am on Tuesday July 17.
A post mortem found Jack died of meningitis and septicaemia following an operation.
Jack's grandfather Chris Carter asked nurse Cooper: "Do all nurses on the ward have sepsis screening training?"
Nurse Cooper replied: "Before this sepsis wasn't on the radar. Now we have got sepsis screening tool to use and if we are concerned we flag. We have had training."
Dr Dudley Bush, who wrote a serious investigation report following the tragedy, told the inquest: "Antibiotics should have been given at 7.50pm on Monday when sepsis was first suspected rather than waiting for the blood tests (results)."
Mr Bush added: "Parents should have been listened to and their views taken into account."
Dr Mike Richards, clinical director at Leeds Children's Hospital, said: "I personally would like to say sorry to the family.
"If there were any actions that we undertook that contributed to Jack's death we are truly sorry."
Dr Richards said lessons have been learned and action has been taken including that sepsis tool is now in use on ward 52 where Jack was treated and across the entire children's hospital.
Dr Richards said: "The sepsis tool is not an answer. It is to raise it as a real possibility to discount as opposed to ignore."
Recording a narrative verdict, senior coroner Kevin McLoughlin, said: "The administration of antibiotics was delayed for some hours that evening after a diagnosis of sepsis was considered, although it's unclear whether this made more than a minimal contribution to the outcome."
Mr McLoughlin added: "Post mortem investigations revealed the presence of an overwhelming bacterial infection on the surface of the brain in the area of the operation site.
"The origin of the infection and the mechanism by which it developed, are unclear."
After the inquest, Dr Yvette Oade, chief medical officer and deputy chief executive at Leeds Teaching Hospitals NHS Trust said: “We are sincerely sorry that Jack died whilst he was in our care and we accept the coroner’s findings.
“We’ve taken serious action to improve awareness and detection of paediatric sepsis since Jack’s sad death in 2018 including increased training and new tools for the early identification and treatment of sepsis. We also launched an annual Sepsis Conference to improve awareness of sepsis, which is free to attend for NHS staff from across the region.
“We have learnt from the findings of Jack’s inquest and will continue to focus on promoting sepsis awareness so that we can provide the best possible care for all of our patients.”