A psychiatrist says it's a "failing of the system" that Oranga Tamariki, the Ministry for Children, does not know how many children in state care have mental health issues or have attempted suicide.
RNZ asked for the figures and was told the ministry did not collate that information, and that it would not provide the data as it would be too much work.
Psychiatrist Siale Foliaki, who works in mental health services in Auckland's Counties-Manukau district, where there are high numbers of children in care, said that "absolutely concerned" him.
Read our investigation into NZ's silent Pasifika mental health crisis: Together Alone
"I know that Oranga Tamariki has come into existence and their principal philosophical position now, compared to the old Child Youth and Family Services, is to absolutely place the child in the centre of care. And if you place the child in the centre of care, that sort of information should be known.
"I think it's a failing of the system to not be able to identify and not to have that type of record so that we could analyse what we do now is better than what we've done before and think about a baseline towards the future.
"If we think that we can do it better, then you should see a reduction in those types of statistics going forward. But how can you make those comparisons if you don't have that information? You don't know where you're starting from."
Oranga Tamariki said it knew young people it worked with often had a complex mix of issues, so it was important that the ministry was vigilant and responsive to potential suicide risk.
The ministry said it kept information about the mental health issues of children on their individual files, and it believed that was the best place for them.
But a veteran social worker and advocate for people who have been in state care, Paora Crawford Moyle, believed Oranga Tamaraki didn't collate the figures in order to avoid painting a desperate picture.
"I actually think that a lot of key information isn't collated, because it reveals too much and it would be too hard for Oranga Tamariki ... to actually explain."
Ms Moyle spent 14 years of her youth in state care, along with her younger brothers, so said she knew first-hand that children in foster homes were vulnerable to mental illness.
"The last thing my Dad ever said to me when he left us was, 'Paora make sure that you look after the boys'. And I took that to mean that was my job, that's what I had to do. I was five years old.
"So when I couldn't do that my mental health, my well-being suffered terribly. Because it's almost like I could handle the harm happening to myself but when my baby brothers were being harmed and they're behind a door that I can't get to because I'm too little to open the handle and I can hear them crying, that is something that stays with you for a lifetime."
Dr Foliaki said the most complex cases he saw were children who were in care.
"They have the most complex sort of needs because they have the least stable environment to return to. And if you think about what causes us to stress - [it's when] we don't feel secure and where do we get our security from? We get our security from strong attachments, strong relationships with primary caregivers with our family.
"So when you remove a child from that... it leaves them more vulnerable than other children."
Dr Foliaki said being separated from your family - even an abusive one - was traumatic and each placement breakdown continued the trauma.
"The challenge for a child is their sense of identity and who they are is always wrapped up in their family. And so the child is always wanting to reintegrate or re-establish contact with their parents and have a relationship with their parents and often it means that they go through an incredibly difficult time emotionally.
"And so a lot of kids go from placement to placement to placement because they're so distressed and a particular caregiver can't manage them. So I see kids in state care and they just get trauma upon trauma and it leaves them really emotionally incredibly fragile."
There is no mental health service that specifically caters for children in state care.
Oranga Tamaraki said it referred children in care with mental health issues to the appropriate services in the community.
But Ms Moyle said that was just rhetoric and she doubted the ministry was doing enough to support the mental health of children in its care.
"I think that there are generic services that they referred to but I hear children saying to me, 'Um actually it goes right over my head. Nobody's listening to me.'
"We hear lots of lovely rhetoric that children's voices are the most important, that we're listening to them, that we're being informed about how we do things differently, how we do things better. I'm telling you, there are a lot of children that are not being heard and there's still those stories and experiences that we're choosing to ignore. That we're choosing to cover up and they're not coming out into the light of day.
"It's not okay to listen to all the lovely stuff and not really take responsibility for some of this shit practice that is actually happening at a frontline level.
"Here's what I think, I don't think that the mental health and well-being of children inside child protection, Oranga Tamariki, are being catered for. I don't think that we have the expertise. We have a lot of incompetence at the frontline."
Ms Moyle said she wanted change within the ministry and has a message for the government: "Stop protecting your own arse! Stop protecting what you didn't get right. Get brave and actually have a look at what we're doing to children in care."
The government's mental health inquiry report, released last week, said many submissions highlighted how childhood trauma was the origin of mental distress and addiction.
The mental health inquiry report also noted that state agencies, such as Oranga Tamariki, could exacerbate trauma.
Despite this, the inquiry offered no specific recommendations for how to support children in care.
This story was made possible by the RNZ/NZ On Air Innovation Fund, the Mental Health Foundation, and the Like Minds, Like Mine programme.