Isaiah Neil's tragic death was needless and the result of "multiple failings" by his parents and grandmother, a court has heard.

Three of the baby's family members were today sentenced for his manslaughter in the High Court at Rotorua before Justice Graham Lang.

Isaiah Neil (also known as Te Whetu) was 8 months old when he died after being left in a hot car while his parents and grandmother smoked synthetic cannabis and passed out at Ruatoki in 2015.

The boy's parents, Lacey Te Whetu and Shane Neil, pleaded guilty on April 27 to manslaughter and grandmother Donna Parangi was last month found guilty of manslaughter after a six-day jury trial.


Parangi and Te Whetu were sentenced to three years' imprisonment. No minimum term was imposed.

Neil was sentenced to one year and 11 months' home detention. He was remanded on bail until a suitable address could be confirmed. His next date of appearance is to be advised.

During sentencing, Te Whetu's lawyer, Bill Lawson, said his client was suffering significant addiction at the time of her baby's death.

"This had an effect on how she behaved ... contributed to distorted thinking," he said.

Lawson said Te Whetu had never shied away from her responsibility and did everything she could once she came out of her drug-induced sleep, including accepting she was at fault for Isaiah's death.

"This has been an event that has entirely turned [Te Whetu's] life around. She is no longer taking synthetic cannabis and is working hard to regain the trust of the authorities so she can be a mother again."

Throughout her lawyer's submission Te Whetu shook and cried in the dock.

Parangi's lawyer, Susan Gray, said the grandmother caused harm by omission, not commission. It was not premeditated but inadvertent, she said.

However, Justice Lang pointed out it was "prolonged" inadvertence. "This isn't 10 or 15 minutes, it was three hours. For three hours, nobody went to check on the baby."

Gray said Parangi maintained care was taken to keep Isaiah comfortable and she only smoked cannabis when she thought the baby was inside.

"Her remorse is genuine, she will live with the consequences of this day for the rest of her life. She will be punished for her actions of that day for the rest of her life."

Gray said it had had a severe impact on Parangi's health, mentally and physically.

"She has been a caring mother, a caring grandmother and a hard-working woman all her life. Her losses have been immense, enormous."

It was Neil who found Isaiah limp, unresponsive and hot in the car around 3.30pm.

His lawyer, Roger Laybourn, said no child should go through what Isaiah went through and Neil said he would "ask the question for the rest of his life why he did not call emergency services".

Experts believed the temperature in the car would have been as high as 45C for between 90 minutes and two hours.

In sentencing the trio, Justice Lang started by saying any death of a child was tragic.

"But it is even more tragic when a child's death is needless and the result of multiple failings by their parents."

He said Parangi's culpability lay not in her decision to leave Isaiah in the vehicle, but that he was not checked on for three hours.

"You minimised the effect synthetic cannabis has on you, saying it had no more of an effect than a cup of tea. You said you hung out the washing and were in the kitchen after taking the synthetic cannabis, but I have no doubt that once you smoked it, you went to sleep.

"By sending your daughter to have a sleep, you were electing to take responsibility for Isaiah. Your culpability is significant in relation to his death."

In sentencing Te Whetu, Justice Lang acknowledged her mother had told her to have a lie-down, but "you were Isaiah's mother. You could have said no, you could have ensured the doors and windows of the car were open.

"When you went to sleep you at least had reason to believe someone else would be looking after Isaiah.

"But your culpability does not end there, like it does for your mother. When Neil brought Isaiah back in and handed him to you while you were very much still under the influence, you put the baby in his cot and went back to sleep for another three hours.

"You failed miserably at this point."

He said it was clear Te Whetu's drug use had had a huge impact on her life and noted her sister took her three children from her care a month before the death of Isaiah, because of her concern for Te Whetu's drug addiction.

Justice Lang concluded Isaiah's father, Neil, had a lesser role to play in Isaiah's death as he had no idea where the baby was.

"You have played no part in the upbringing of the child and did not know where he was.

"Your culpability lies in that you discovered Isaiah in a clearly unwell state. Emergency services should have been called immediately, but unfortunately you had consumed synthetic cannabis as well and your judgment was clouded."

There are no minimum sentences for manslaughter cases, which means judges can impose sentences that differ depending on the circumstances.

Two years ago, a health professional in Whanganui was discharged without conviction after pleading guilty to the manslaughter of her 16-month-old son.

She accidentally left him in the car in January 2015 and he died of dehydration and heatstroke.