Police won't be laying any charges over an incident last year in which three Porirua children were rushed to hospital in a near-comatose state after ingesting synthetic drugs.

They have also revealed the children probably ingested the deadly drug after their dinner was cooked with a contaminated utensil.

More than a year on from the incident - during which an 8-year-old boy had to be placed in an induced coma for several days - police have confirmed no charges will be laid.

Detective Senior Sergeant Neil Holden said police believed they had figured out "what hasn't happened".

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"If we had belief or evidence there was an intent, then charges would follow," he told the Herald.

"The police are of the view that there was no intentional administering of substances to anybody in the family."

The children, then aged 5, 8, and 14, were taken to Wellington Hospital in September last year after apparently consuming the substance with their dinner.

"While initial medical concerns were significant, with proper medical care each child made a full recovery," Holden said today.

"Wellington Police Child Protection Team have completed their investigation and believe traces of synthetic drug material were on a cooking implement that was later, inadvertently, used for food preparation at the children's home."

Police believe the contaminated cooking implement had been used to make the synthetic drug, but have not been able to ascertain who did it.

The children were all from the same family. An ambulance was called by the children's mother when they began to show the effects of ingesting the drug, Detective Senior Sergeant Grant Ferguson said at the time.

"By the time they all arrived at hospital their condition was described as almost comatose. One child in particular was having difficulty breathing."

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About a month and a half after the incident, Holden said the children had made a "remarkable recovery", though the long-term effects remained to be seen.

Holden said police wanted to reinforce the dangers of all drug taking and production, especially around children and vulnerable people.

New Zealand Drug Foundation executive director Ross Bell said cases such as this were "absolutely shocking".

"You have adults who are in a position of responsibility ... they're living such a life that they do really dangerous and dumb things like manufacture really dangerous chemicals in a place where young children are.

"It's such a challenging issue because quite often adults who do that have problems being responsible adults, whether it's because of their addiction or other wider issues. It puts young people at significant risk."

One of the issues with synthetics was that people were unaware of what chemicals they were using, he said.

They would often arrive in the country in powdered form and people would "cook these things up".

"Often people don't know what the chemicals are and how dangerous they are. They're wanting to make a quick buck.

"These chemicals are inherently dangerous and clearly when done in a household in someone's kitchen it can have really dire consequences."

Bell said people were aware of the danger of synthetics but were still using them, so telling them to stop was not going to work.

Instead more support needed to be given to services dealing with drug users, who could find out what was needed to help people make different choices.