The father and mother were sentenced to six and five months home detention respectively at Rotorua District Court.

The children were sat in the back of the car, their faces dirty, mucus coming from their noses and the boy - just three years old - naked apart from a singlet.

Their parents were in the front. Mum was asleep, dad unconscious, 'bong' in hand.

They'd been there from about 2am to 8.10am, when a passer-by knocked on the car window, alarmed at the sight he first saw two hours earlier.

It was a December day in Tokoroa, and the passer-by, on his way for an early morning swim, had chanced upon yet another case of child ill treatment, fuelled by synthetic cannabis.

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CHRIS SKELTON/STUFF The father of a two and three-year-old admitted he knew the synthetic cannabis smoke could harm his kids, but he did it anyway.

The parents of the two and three-year-olds, who cannot be named to protect the identity of their children, were sentenced earlier this month, almost a year after their 2017 offending. They appeared at Rotorua District Court, each on two charges of ill treatment of a child.

Sentencing the pair, Judge Tony Snell was scathing about their conduct.

"Those children rely on you. They're two and three, they cannot care for themselves. It's your job to look out for them, not to put them in danger."

He also referred to the mother's pre-sentence report in which she said she had considered the possible consequences of smoking synthetics around her children in an enclosed car - but did it anyway.

"A reprehensible act of self interest," said Snell.

According to the police summary of facts, the children were exposed to the synthetic cannabis in a car over two occasions, the first time being found by the passer-by.

On that occasion police were alerted and the father, in the driver's seat, was found to be "only able to reply through groaning noises".

"At this point he had possession of the bong in his hands."

A search of the vehicle located a small plastic bag containing plant material "similar in appearance to that of cannabis".

The officers also found the dishevelled children, taking them and their mother home.

Remarkably, just three days later an identical offence was committed. With the father driving, mother in passenger's seat, children in the rear with the father's sister, they parked on a quiet Tokoroa street.

"Utilising a large bottle [they] began consuming synthetic cannabis in the vehicle."

The summary revealed the sister asked them to stop - and wound down the windows in the back in an attempt to protect the children from the smoke.

"They ignored her and carried on."

The father then drove the car to purchase more synthetic cannabis, consumed more of it, then fell unconscious.

"At this point three-year-old [the boy] was crying and yelling at [his mother], he was hitting her from behind in an attempt to wake her."

The sister, concerned about the behaviour she was witnessing, had by this point phoned her parents who arrived 30 minutes later to find the father slumped in the front seat, and the mother "gone".

The father - who had began to wake - then drove with the children in the car to the mother's residence.

In comments to the police, the father admitted using synthetic cannabis.

"He also conceded that this would be detrimental to their [the children's] health."

That decision to drive was later described by Snell as "appalling".

He noted the father has 15 previous convictions, mostly for domestic violence, and that in his stupor "wouldn't have had a clue" who initially removed his children from the car.

"Driving them around when you couldn't stand up. Ridiculous behaviour."

Snell's stance softened however when he revealed both parents had successfully proved to be clean of alcohol and drugs, and were taking part in rehabilitation programmes.

He said home detention - the father received six months and the mother five - would "give you the tools to not go back where you have been".

"You are deficient in a significant way and need a lot of tools to be a good parent."

Speaking after the sentencing, the mother's lawyer Arama Ngapo-Lipscombe, said her client was embarrassed by her offending - and determined to turn her life around.