The couple were pursuing legal avenues to gain formal custody of the children, said Barnett.
"They are looking after the kids and she wants them back," Barnett said.
Barnett added Nikau was upset about the incident. "He's disappointed at what's happened."
Huntly resident Polly Nepe, who took in Heaven as a boarder for more than a year, said she was looking after the kids last weekend when Heaven arrived demanding to take them.
"Heaven said she wasn't going to give them back. That's how this whole thing happened. I feel a bit responsible because they were taken from my home." Nepe said Nikau had come to her house the following day trying to find the children, and had been upset.
"We tried to calm him down but he was pretty angry. He said that it's her that's causing the trouble."
Yesterday, the Herald on Sunday was buzzed through secure gates that led to Nikau's sprawling mansion in Ohinewai but then met with a cold reception at the front door.
A young man said Nikau was not at home, despite three black 4WDs, including a company car for Aotearoa Construction, filling the garages.
He refused to pass on a message to Nikau saying, "no, we don't want it," when handed contact details. Young children could be heard in the background.
A few kilometres down the road his brother, Victor Nikau, did not know about the incident but said, "has this got something to do with his daughter?"
Several family members drinking at the local pub were surprised and disappointed about the assault charge.
They said Nikau had a placid nature and always "spoiled" his children, especially since their mother died.
A cousin, who asked not to be named, said Heaven was a "drama queen" who would have triggered her dad's anger. However, she said it was no excuse for the alleged assault.
Waikato police said in a statement that a 45-year-old male was arrested outside the Huntly Police Station on Friday afternoon over a domestic assault. They gave no other details.
Witnesses told the Waikato Times Nikau, 45, grabbed a woman by the neck, causing her to fall to the ground.
Sir Peter "The Mad Butcher" Leitch got behind Nikau last night: "The man I know is a wonderful, wonderful person who I would go to war for.
"I love him dearly, he's never turned down any charity work.
"Irrespective, he will always be the Mad Butcher's friend."
