Lachie Jones was found dead in an oxidation pond on January 29 in 2019, but how he got there remains the subject of some conjecture.
The initial police investigation concluded the boy had walked the 1.2km from where he was last seen and tragically drowned, but his father Paul Jones has always disputed that version of events.
It was ordered to pay reparation to Lachie's parents, but Mr Jones said he did not blame the council.
The boy's mother - whose name is suppressed - is giving evidence at the Invercargill District Court today, but this will remain under wraps until she has been questioned.
Coroner Alexander Ho opened the hearing by expressing his condolences to Lachie's family and friends.
"The loss of a young life like Lachie and the impact this would have had on you is unimaginable to those not in your position," he said.
"No condolences I express here today, while genuine, can salve your grief. I did not have the privilege of knowing Lachie but he's now my responsibility."
He emphasised that two police investigations found there was no nefarious involvement of any other person in the boy's death.
But the coroner said he was not bound by that.
If he found there was a likelihood of illegality, that would be a matter for police.
"Here, we're conducting a fact-finding exercise," Coroner Ho said.
The inquiry will consider the cause of death and the circumstances that led to Lachie ending up in the pond, including whether neglect was involved, and the coroner may make recommendations to prevent similar deaths.
The first phase of the hearing is set down for three weeks.
