A woman accused of the manslaughter of her 8-month-old grandson made a fatal decision when she chose the consumption of synthetic cannabis ahead of the care of her mokopuna, a jury's been told.

Prosecutor Anna Pollett made the claim in the High Court at Rotorua today where Donna Catherine Parangi, 48, of Ruatoki, is on trial for the manslaughter of Isaiah Neil in November 2015 by depriving him of the necessities of life and failing to take reasonable steps to protect him. She has pleaded not guilty.

The baby's parents, Lacey Te Whetu and Shane Christopher Neil, earlier pleaded guilty to manslaughter.

It's alleged Parangi and her daughter, Lacey Te Whetu, left Isaiah Neil in a hot car with the windows closed for at least three hours while they indulged in the synthetic cannabis they'd bought that day from Parangi's Kawerau dealer.

Advertisement

The first Crown witness, Kylie Te Whetu, another of Parangi's daughters, said she'd taken her sister's two older children with her to Auckland because of her mother and sister's "stoned states".

She described seeing them zombie-like, not able to do much and, on occasions, unable to wake up. She wept as she described Isaiah as a happy child who was very easy to look after.

Dabbing at his eyes her brother, Marcus Te Whetu, said when his mother told him the infant had not woken up he was disappointed, upset and really mad that the baby hadn't been looked after in his absence ... that everything was good when he was around.

Mr Te Whetu said he knew there was synthetic cannabis in the house outlining how, when he asked his sister questions, she didn't respond and would bump him out of the way as she walked past him at speed.

Asked about his mother, he said she worked long hours and enjoyed a couple of beers at the end of the week.

His partner, Felicia Riini, told Ms Pollett she knew for a fact there was synthetic cannabis in the Te Whetus' Ruatoki home.

"I have seen it with my own eyes," she testified.

She said when she first asked Parangi how Isaiah had died she said he passed away in the car but later on the marae changed her story to say he died in his cot.

Questioned by defence lawyer, Susan Gray, she said Parangi worked full time and long hours, that it was Lacey who prepared her son's food, changed his nappy and generally tended to his needs.

At the start of the trial Justice Graham Lang warned jurors not to be influenced or prejudiced about drugs, saying drug use played an important part in the trial and whether they impacted on the care of children.

Opening the Crown's case, Ms Pollett claimed through their drug use Parangi, her daughter and Neil played Russian roulette with children in their care, Isaiah included.

She outlined how, around 9.30am on November 2, Parangi and Te Whetu took the baby with them to buy $40 worth of synthetic cannabis.

It was a hot day, and once home they left Isaiah asleep in the car with the windows up while the trio smoked until they fell asleep. At no stage did they check on the baby.

Ms Pollett said it wasn't until other children returned from kohanga reo and Neil woke up that he took Isaiah out of the car, where he'd been at least three hours.

Despite finding him hot, sweaty and unresponsive he'd done nothing for the infant or called emergency services. Instead, he'd put him beside his sleeping partner where he'd remained for another three hours.

When an ambulance was finally called it was discovered Isaiah was dead from heatstroke.

Ms Pollett said evidence would be called that the child would have died within 45 minutes inside the car.

She contended Parangi had actual care of, and responsibility for, her grandson saying both she and her daughter consumed the synthetic cannabis "without concern for baby Isaiah".

"The fatal decision she made along with her daughter was the consumption of synthetic cannabis over the care of her mokopuna."

Ms Pollett said a large bruise and other non-accidental injuries were later found on the infant's body.

Defence lawyer Susan Gray disputed the crown's claim Parangi departed from the standard of care expected, saying the main issue would be whether she was in the state of a parent at the time Isaiah died.

She asked the jury to note the parents' guilty pleas, saying these were entered because they were the ones who had care of him but failed him.

She also took issue with the crown's contention that Isaiah had died from heatstroke.

"The defence says this is far from clear."

The trial is expected to last two weeks.