A string of blunders by NHS workers led to the death of a three-year-old boy, a review has found.
Sam Morrish died from a treatable condition because four separate health service organisations made repeated mistakes in his care, the Parliamentary Health Service Ombudsman (PHSO) said.
Sam died of severe sepsis in December 2010 following a "catalogue of errors" by the Cricketfield GP Surgery, by NHS Direct, by the out-of-hours service Devon Doctors Ltd and by the South Devon Healthcare NHS Foundation Trust.
Failures included inadequate assessment of the toddler, not recognising that he was vomiting blood and a three-hour delay before he received antibiotics at hospital.
But his family said as well as losing their son, they feel they have been "failed" by the NHS complaints system.
In a statement released through the Patients Association, they said: "The astonishing length of time it has taken for PHSO to finalise this report has inescapably prolonged our distress, as we have repeatedly had to revisit and relive the hardest day of our lives.
"Accordingly, although we are grateful that the PHSO has upheld our complaints, and we want to thank them for the clear recommendations that they have now made, we are left with serious concerns about the competence, capability and accountability of the PHSO itself.
"We pursued our complaints because we wanted to reduce the likelihood of the mistakes that were made in Sam's care, and the subsequent investigations, from being repeated.
"This was not only for the individual organisations that made those errors - but for the NHS as a whole.
"We never have been interested in blame. We have only ever been interested in learning and understanding, in the hope of change wherever necessary.
"Clearly we feel the complaints systems failed us, but it is important to note that we also believe it failed NHS staff too."
The family added: " Now the report has been published we hope that we will be free to concentrate on our futures, and on remembering our beautiful, sparkling, affectionate little boy, who we continue to miss every day."
Ombudsman Dame Julie Mellor said that had Sam received the appropriate care, he would still be alive today.
She added that Sam's devastated family suffered "further injustice" because health officials failed to properly investigate the youngster's death.
Dame Julie said: " We've published this case so that the wider NHS learns from Sam's death and action is taken to help prevent lives being lost from repeated mistakes.
"Sadly, this case reinforces that the NHS needs to do much more to prevent avoidable deaths from sepsis."
NHS England should make a payment of £20,000 to the boy's family "in recognition of the missed opportunities to save the boy's life", a spokeswoman said.
Dr Graham Lockerbie, speaking on behalf of the local NHS, said it is " determined to ensure that the lessons really have been learnt".
He added: "Sam and his family have been let down by the NHS. It's clear that there were shortcomings at every stage of his contact with the health service and that, in the words of the Ombudsman, Sam died when he should have survived.
"All of the organisations involved recognise that opportunities to alter the tragic outcome were missed. We all accept the blame for that. For this, we, the local NHS, apologise unreservedly to Sam's family. Quite simply, we should have done better.
"When we investigated, we were still unable to provide adequate answers to Mr and Mrs Morrish about what had gone wrong, or to reassure them that things would change for the future. It is clear that this only compounded their grief. Again, on behalf of the local NHS, I apologise."
According to the UK Sepsis Trust, the condition claims 37,000 lives in Britain every year.