The deaths at Sanson are being treated as a murder-suicide, RNZ understands, although police are yet to confirm that.
Manawatū Area Commander Inspector Ross Grantham said the father was not burned - but his three children, aged 1, 5 and 7, were.
It is understood the father was Dean Field, and the children have been named in the Givealittle campaign for their mother as August, Hugo and Goldie.
The bodies of two children were recovered on Sunday night and were blessed by the family with karakia. The body of the father was removed earlier.
The third child's body was recovered on Monday morning, Grantham said, by investigators supported by a forensic pathologist.
The children's family were present as the child was taken from the scene, he said.
Grantham said the next few days would be a "hard grind" for police examining the site, and talking to witnesses and whānau.
Meanwhile, by 9am on Tuesday more than $260,000 had been raised for the mother of the children as she deals with the "unimaginable loss".
"They were the light and love of her life, and her entire world has been shattered," the Givealittle page said.
"In the midst of this unimaginable grief, she also lost her home and everything she owned. She is facing the hardest journey possible, stripped of her physical security, while navigating the deepest emotional pain."
The creator of the Givealittle page posted a thank you to "what felt like the whole of Aotearoa" on Monday for the donations raised.
"No amount of money will ever be enough to heal the wounds left in her heart and soul, but to have this safety net to rebuild her life, knowing what feels like the whole of Aotearoa is with her, and how you have all contributed to this outpouring of love in so many ways is more than we could've ever hoped for."
Speaking to media on Monday, Grantham said it was too early to tell if the fire was deliberately started.
"It's pretty risky with the part of the structure still there and the the dust that's generated from the fire, so it will take us some time just to go through and establish what's happened."
Grantham said police were not seeking information from the public at this stage, but if anyone knew anything, they could "reach out".
He said it was "unusual" for a house fire to begin in the afternoon.
Police would remain at the property for "as long as it takes", Grantham said.
Where to get help:
- Need to Talk? Free call or text 1737 any time to speak to a trained counsellor, for any reason.
- Lifeline: 0800 543 354 or text HELP to 4357.
- Suicide Crisis Helpline: 0508 828 865 / 0508 TAUTOKO. This is a service for people who may be thinking about suicide, or those who are concerned about family or friends.
- Depression Helpline: 0800 111 757 or text 4202.
- Samaritans: 0800 726 666.
- Youthline: 0800 376 633 or text 234 or email talk@youthline.co.nz.
- What's Up: 0800 WHATSUP / 0800 9428 787. This is free counselling for 5 to 19-year-olds.
- Asian Family Services: 0800 862 342 or text 832. Languages spoken: Mandarin, Cantonese, Korean, Vietnamese, Thai, Japanese, Hindi, Gujarati, Marathi, and English.
- Rural Support Trust Helpline: 0800 787 254.
- Healthline: 0800 611 116.
- Rainbow Youth: (09) 376 4155.
- OUTLine: 0800 688 5463.
If it is an emergency and you feel like you or someone else is at risk, call 111.
