Oranga Tamariki will not say how long it has been involved with the family of two young siblings thought to have been deliberately injured in Lower Hutt.
Police are appealing for information on how a four and five-year-old suffered injuries so horrific they needed hospitalisation and surgery.
The family moved to Stokes Valley just days before the children's injuries were discovered by medics in early February, when one of the siblings was taken to hospital by ambulance.
Detective Senior Sergeant Rebecca Cotton confirmed on Friday that the family were known to police and Oranga Tamariki, but Oranga Tamariki deputy chief executive Rachel Leota said she could not provide any further information.
"Oranga Tamariki acknowledges the incredibly distressing nature of this and would encourage anyone with information to contact police," Leota said in a statement.
"We are working alongside police in relation to this matter, because of this we cannot provide further detail at this time."
The agency did not answer RNZ's questions about when it first become aware of the children, what the circumstances were, and any actions it had taken.
'Speak up,' child advocate urges
Anyone who knows about what had happened to the two children is being urged to come forward by an advocate for child abuse prevention.
Child Matters chief executive Jane Searle said it was important for people to share anything which could help police.
"Though it is difficult for people to speak up and co-operate with enquiries such as this we need to remember that children cannot stop abuse, but adults can," she said.
"For those responsible to be held accountable, that means there are adults who are going to need to step up and to play their part by saying what they know."
Searle, a former police detective, said child abuse investigations could be difficult - particularly when people were not being forthcoming.
"It is common in these sorts of enquiries for people not to fully co-operate with police, and that's what makes them such difficult and complex inquiries.
"I think we shouldn't underestimate the effect that has on how much longer these inquiries can then take."
Child abuse prevention authorities needed better co-ordination and resourcing, Searle said, because it was clear the the system was not robust enough.
"We've known for a long time that New Zealand does not have a good record when it comes to protecting its children and young people, and it's something we need to have increased focus on because it has not got any better," she said.
"This is not the first case we have seen and, unfortunately, we know for a fact it will not be the last, so that's why it needs increasing priority.
"When we have children who are on the radar of Oranga Tamariki or the New Zealand Police, we need to have a system that monitors their well-being in an ongoing way. It takes resourcing and it takes a huge amount of co-ordination of the system, but we've got to keep improving the system or we're going to continue to have cases such as this."
A community hurting
Meanwhile, the Hutt Valley community was reeling after the second serious child abuse case in the area in less than six months.
It has been five months since Taita toddler Baby Ru died of head injuries in October, and police are yet to lay charges.
Northern ward councillor Naomi Shaw - whose area covers Stokes Valley and Taita - said she was saddened by the latest incident.
"To hear that a four-year-old and a five-year-old, who haven't even reached school-age yet, have been physically abused over a long period of time, just makes you feel sick, it really does."
The community was still grieving over the death of Ruthless Empire, she said.
"People were really upset, genuinely upset, especially when it comes to children - and that would be the case in any place in New Zealand.
"They're still reeling from it, and that's exactly what I thought straight away when I heard about this one. Two more children involved in a serious assault. It's just not on, it's not okay."
Shaw was unsure how long the new investigation would take, considering there was yet to be a resolution in the Baby Ru case.
"I guess that's at the back of our minds. It seems like we have had a lot going on in our little community.
"The police are diligently doing their job and they're trying to do their best - they have to make sure that they get it right so they can nail the people responsible," she said, adding that she was sure the officers working both cases would be "as saddened and sickened" as the rest of the community.
Police asked anyone with information to call 105 and quote file number 240308/4647, or call Crime Stoppers anonymously on 0800 555 111.