A support worker did not attend, and the boy was left at the terminal on his own, until a member of the public noticed the boy by himself and telephoned his mother for him, the report said.
The disability service conducted an internal investigation, which found that the scheduled support worker had advised the care coordinator that he would be unable to attend the shift.
The care coordinator had taken actions to book a relief support worker, however they did not communicate with the proposed relief support worker or inform the boy's mum of the changes to the shift, the investigation found.
Following the internal investigation, the boy's mum made a formal compliant to the HDC, which conducted its own inquest.
Deputy commissioner Rose Wall, who found the breach, was critical of the support worker, saying: "While the care coordinator's error was administrative and unintentional, it was a fundamental aspect and requirement of her role, and resulted in the boy being placed in a vulnerable and potentially dangerous position."
Wall recommended that the care coordinator provide HDC with her reflections and learning from the incident, and provide a written apology to the boy and his mother.
While the disability service was not found in breach, Wall considered that valuable learning could be taken from the case.
She advised that the disability service provide HDC with an update on changes taken to improve systems for arranging relief support workers.
The care coordinator, who was less than three months on the job, said she had no doubt that her mistake caused this and she deeply regretted it.
The disability service sincerely apologised that the individual actions of the care coordinator resulted in the boy being left in a vulnerable position, and for the stress and anxiety created for the boy's mum at this time.