Almost 80 children have died in the care of the New Zealand state in the past 15 years - an average of five a year.
Data released by the Ministry of Social Development under the Official Information Act show that 38 children died of natural causes while in state care, 19 died in accidents, 14 committed suicide and six were victims of child abuse, homicide or manslaughter.
The worst years were 2004-05 and 2006-07, when nine children died in each year.
The latest year, 2014-15, was the only year when there were no deaths.
The deaths were a tiny fraction of the total numbers of children in state care, which have averaged about 5000 throughout the past 15 years.
But Otago University child protection expert Dr Nicola Atwool said they showed that taking children out of their families was no guarantee that they would be safe.
"There are a lot of people who think bringing children into care is the answer, but it isn't," she said.
"It can be, but we haven't got care right in New Zealand, and the vulnerability of abuse is actually compounded by coming into care."
Ministry of Social Development deputy chief executive Murray Edridge, who released the data, said some of the children who died "came into care because they were born with, or developed, a terminal illness or other complex health needs or disability that required specialist care":.
"All deaths by suspected homicide are investigated by the Police," he said.
"When a child or young person involved with Child, Youth and Family [CYF] dies as a result of suicide or homicide, the Office of the Chief Social Worker examines each case and provides a report... This report is also provided to the Children's Commissioner."
However the deaths were just the tip of a larger iceberg of children abused while in state care. The data disclosed 550 cases of substantiated abuse of children while in CYF care in the five years to June last year, an average of 110 cases a year.
The abuse was committed by CYF-appointed foster parents in about a third of the cases (187).
Other perpetrators were biological parents and other family members while their children were home on contact visits (164), staff of contracted support services (44), CYF staff (6) and "others" (149), who included the children's friends and relatives and other children in their foster homes.
Out of 402 perpetrators in the three years to June last year, no charges were laid in half the cases (207).
Charges were laid in 101 cases. Of these, 27 perpetrators have been convicted, nine were acquitted, and 65 cases were still pending at the point when the cases were recorded. Edridge said the ministry might not have had the latest information from police in all cases.
Police were still investigating another 56 cases at the time they were recorded, and no information was available for the remaining 38 cases.
Atwool said the abuse in state care heightened the need to work with families to stem the flow of children into care.
"If we can get into the families early enough and do the work to get the families on the road to change, that's where you will see your long-term dividends," she said.
She was "heartened" that the new Ministry for Vulnerable Children Tamariki Ora would have dedicated work teams for early intervention and for children in state care.
"We have got to get both right," she said.
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