Neighbours are shocked and confused after hearing a baby girl from a "lovely" everyday family died after being assaulted.

The 6-month-old girl died in Wellington Hospital last night after being airlifted from her Kapiti Coast home in a critical condition on Monday.

Friendly residents of the Raumati Beach neighbourhood were still struggling to absorb the news today and said nothing so awful had ever happened in the street before.

One neighbour, John Ivor, said he couldn't get his head around what happened.

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"It's just so bizarre," Mr Ivor said.

"They're fine. They seemed like you and me, everyday nice people."

He believed the family had not lived at the house long, probably less than two years.

Mr Ivor said he was dumbstruck after learning why police cars arrived across the road on Monday afternoon.

He said he didn't know the family well, but they'd always greet him when he walked past.

He said his neighbour also had only good things to say about the family.

He said the family kept pets, including guinea pigs, and were friendly.

"They just seemed like really nice folk ... what the heck has gone on?"

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Neighbours Gabriella Monaghan and Liz Boyd were also shocked to hear of the baby girl's death.

"There's nothing mean to say about them. They're so nice," Ms Boyd said.

She wanted to extend her condolences to the baby girl's family, who were always pleasant and never caused any trouble.

"They just must be suffering so much..."

Ms Boyd also had only good things to say about the family and was in disbelief.

Another neighbour said the baby's death was the worst thing that had happened in the 29 years he'd lived in the neighbourhood.

He said the family were "very lovely" and never caused trouble.

A 31-year-old man appeared in Porirua District Court today charged with assault. He was remanded in custody until Friday.

Interim court suppression orders prevent publication of the defendant's name.

The orders also ban publication of the girl's name, or of details that would identify her or her family to the general public.

A police scene examination was still underway at the Raumati Beach property tonight, with several security company vehicles on site and the house cordoned off.

A child's toy car was at the house.

Some distressed neighbours asked if the little girl's death was part of a wider social problem, following news of another baby dying violently in the past week.

Christchurch 15-month-old Ihaka Paora Braxton Stokes died after suffering injuries including broken bones on Friday night.

Detective Inspector Greg Murton said today that post-mortem results showed Ihaka died from multiple blunt force injuries and was the victim of an "extremely violent assault or assaults".

Police and St John were called to the house at Truman Rd, Bryndwr about 10.30pm on Friday. Ihaka was found unconscious with unexplained injuries.

He was transported to the accident and emergency department at Christchurch Hospital and died shortly afterwards.

Mr Murton said officers had spoken to "quite a large number of people", including the boy's mother and stepfather, who lived at the address.

He refused to say whether either of them were suspects.

Former Families Commissioner Christine Rankin said tonight it was clear not enough was being done to stop a "sickening" spate of child abuse.

Ms Rankin said New Zealand had made no headway on the issue, despite multiple cases of kids being killed.

She said New Zealand's child abuse rates were "embarrassing" and anti-smacking legislation had not addressed the problem.

"This is vicious, violent, regular beating. Unfortunately we've got a group of people in New Zealand who do it. It's getting worse."

Ms Rankin said if 20 politicians were killed each year, there'd be an unprecedented review and bout of soul-searching - but when 20 children were killed in a year, nothing was done.

She said lawmakers had tightened up penalties for child abusers slightly, but in some case tougher penalties were needed to keep violent adults away from kids.

"You hurt your child, you don't get it back," she suggested. "That doesn't happen in New Zealand."

- Additional reporting: Kurt Bayer