By morning, the boy's condition deteriorated rapidly and tragically he died.
The cause of his death identified at post mortem was bilateral pneumococcal pneumonia.
Deputy Commissioner Rose Wall was critical of the DHB, saying there were multiple failures in the care provided to the boy.
"Staff made assumptions, including that the boy's illness was pneumonia without sepsis."
She said if his condition had been recorded correctly he would be reviewed promptly during the morning ward round.
"It is impossible to know whether the outcome would have been different if these errors had not occurred.
"However, I consider that the above failures resulted in a lack of recognition and response to [the boy's] serious illness and the emerging signs of his deterioration," Wall said.
She also found that nursing staff failed to think critically about the boy's overall clinical picture and, as a result, failed to escalate his care appropriately.
"Medical staff failed to consider the overall clinical situation and to explore the possibility of sepsis more thoroughly; and there was a culture of non-compliance with the PEWS management plan by nursing and medical staff."
Wall was also critical that when the boy presented to the medical centre the second time, pneumonia was not included in the differential diagnosis and no further observations were recorded in the clinical notes.
The deputy commissioner recommended that the DHB provide evidence that all the recommendations from its Serious Event Review had been actioned and their impact evaluated.
She also told the DHB to provide further training to paediatric nursing and medical staff and consider whether a review of its health pathway for administering oxygen therapy was warranted.
The medical centre was also told to provide training to clinical staff on the recognition and treatment of sepsis in children, and a written apology to the boy's parents.