A person in Lower Hutt, where two young siblings were severely injured, has come forward to police.
Two Lower Hutt children, aged four and five, were hospitalised with "very, very severe" injuries believed to have been inflicted deliberately over "a long period of time", police said on Friday.
One had "brain bleeds and severe internal injuries".
Detective Senior Sergeant Rebecca Cotton says the information the person had provided would help police enquiries.
No arrests have been made and no charges had been laid, police said.
The investigation into how the children's injuries were sustained was progressing, she said, but police continued to have "varying degrees of engagement" from the family.
Cotton said the siblings are recovering well since they were discharged from hospital.
The police continue to appeal for witnesses to come forward.
Police said the children's family had recently moved to Stokes Valley and had been in their new home just two nights when the children were hospitalised.
They were known to both Oranga Tamariki and police, who had visited the home previously.
Kāinga Ora said the case was not related to any of its houses.
Lower Hutt Mayor Campbell Barry said the incident was "absolutely horrific".
He said there was a strong feeling from residents that anyone with information needed to come forward.
"This is obviously not the first time a type of incident like this has occurred," he said.
"But when you have innocent children sustaining these types of injuries, there's just no excuse."
Barry said even the smallest bit of information may help.
"Anyone who has information, no matter how small that may be, out in the community that may be of assistance, we're really encouraging them to speak with police."
Remutaka electorate MP and Labour leader Chris Hipkins said the tragedy was disturbing for the community.
"I know from the feedback that I've had around the local neighbourhood that people have been pretty shocked by this and shocked to think that it could be happening in a household in their neighbourhood."
He said there was too much family harm in New Zealand.
"We need to work really hard to make sure that we are changing our culture so that it doesn't go undetected so that it is called out and so that we are doing something to change that. These children deserve a much, much better life than this."
Women's Refuge chief executive Ang Jury said society was letting children like this down and people needed to speak up.
"Oranga Tamariki and police would far rather that you reached out to them with something that turned out to be nothing than having to attend things like they have out in the [Hutt] Valley over the last few weeks."
