He said there was a clear link between poverty and violence against children, with "dreadful outcomes".
"Children in the poorest 10 per cent of the population are 10 times more likely to be admitted to hospital with an inflicted injury than children in the wealthiest 10 per cent of the population."
The effect of child poverty was usually life-long.
A child's brain developed quickest in its earliest years but it was also at its most vulnerable.
"That's when poverty, and the stress related to it, does the most harm.
"We know from our own experience and from published evidence there are a group of very poor children who are arriving at school aged 5 with language of 3 or 3-and-a-half-year-olds. So they are well behind their peers.
"If you arrive at the language of a 3-year-old you are very unlikely to leave schools with qualifications.
"Our schools' students do remarkably well, except for that group of students that get left behind.
"So the time in your life that an investment is going to make the biggest difference to whether you leave school with qualifications or not, is in the first five years.
He said the Government was already investing in that group, which helped and needed to continue, but the investment had less impact while families were poor and living in "crowded, cold, damp houses". He said while New Zealanders were "smart and care deeply about children," we had not done enough about the issue. "Once people understand it better, then there will be a strong support for the kinds of recommendations made by the [Children's Commissioner] expert advisory group in December on solutions for child poverty."
Many of the recommendations "are quite difficult policy choices", calling for targeted spending, "particularly more on our youngest and poorest children, because that's where a dollar makes the biggest difference".
The advisory group recommended a plan to deal with poverty "and material deprivation".
"The stuff we simply can't afford, like toys or petrol for the car to get to the library or playground."
The cost to the economy was 3 per cent to 4 per cent of GDP - $6 billion to $8 billion a year, he said.
"Child poverty doesn't just cost those kids - though that's terrible - it actually costs all of us.
"So if we choose to reinvest that money in the people to whom it will make the biggest difference, it will be in the kids whose brain development is harmed by poverty.
"Those children will benefit but so will the whole of society."
Recently retired HBDHB board member and paediatrician Dave Barry said while the country's health service did "pretty well" it could not address the social aspect of health.
He said there was a clear cycle.
"If you are poor, then the chances are your parents are poor and not well educated, so they don't see the value of education and can't support you in your education."
The situation was getting worse, with the middle class shrinking as the gap between rich and poor widened, he said.
"The poorer people are more likely to be unhappy, to be on drugs and have those sorts of things occur in life that would make them vent their frustrations as physical abuse."
Government policies were not helping poor people.
"The Government's view is that you can get economic growth then all else will come, but it has never worked that way. A powerful economy like India has dreadful poverty.
"Economic growth alone doesn't do it.
"You have to make some changes in society to even out incomes.
"Scandinavian countries do that. They don't tax the rich to death and have a more even distribution.
"The United States, which unfortunately seems to be our economic model, is worse than we are."
New Zealand's worsening child health outcomes had brought the country to the attention of international groups such as Unicef.
Monday's report is the inaugural Child Poverty Monitor, a collaboration between the Office of the Children's Commissioner, the University of Otago's NZ Child and Youth Epidemiology Service and the JR McKenzie Trust.
On Monday, Dr Wills will release a report on the effects of child poverty.
