Dr Russell Wills' term as Children's Commissioner ends on June 30.

In 1993, New Zealand ratified the United Nations Convention on the Rights of the Child. The Convention describes fundamental rights all children should expect in a civilised country. One of these is the right to an adequate standard of living, including a home.

We don't know how many children are currently sleeping in cars, garages, tents, caravans or shipping containers, nor how many are "couch surfing", with no home of their own. But it is much more than the 480 that Work and Income know of.

Here's what we do know: 50 per cent of Pasifika children and 25 per cent of Maori children live in crowded homes. Forty per cent of families on low incomes spend more than 30 per cent of their weekly income on rent. In South Auckland, rents have increased 25 per cent since 2010, so typical rents for a three-bedroom house are about $400 a week.

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While the population has grown, the number of state houses has remained the same, at around 69,000, leaving 20,000 fewer houses per capita compared to 1991.

The Salvation Army estimates around 10 per cent of garages in South Auckland are being used as a residence.

We know that large numbers of children are affected by poor housing, or no housing at all, because they get sick and are admitted to hospital - some 42,000 children a year and, we estimate, 15 deaths a year. I can't tell you how heart-wrenching it is to admit a child to hospital with a chest infection, treat them, and send them back to such conditions. Yet this is the grim reality for paediatricians now, particularly in Auckland.

I talk to Work and Income staff every week to see what we can do to help the families whose care we share. My experience is that they are good people who do everything they can, but the houses are simply not there. Offering a loan for a motel that has to be paid back makes little sense, but sometimes there isn't much else they can do.

I'm pleased the Government has announced $41 million to pay social agencies for the emergency housing they are already providing. That at least means they won't have to close their doors, but it creates no new housing.

Other countries invest more in social housing (low-cost housing provided to people on low incomes who would otherwise be at risk of homelessness) than we do. In the UK and Scandinavia it's 17-22 per cent, in the Netherlands 34 per cent. So what can we do about the lack of social housing in New Zealand?

The Expert Advisory Group on Solutions to Child Poverty said there is a fundamental flaw in our thinking of social housing as social spending. In many countries, social housing is instead considered core infrastructure, like roads and airports.

The main reason for this is that it allows policy makers to plan for and invest in housing, public transport and services like schools and playgrounds together, so we don't get behind in any area, as we so clearly have with housing.

It also means social housing can be planned for alongside privately owned and rented housing, and can be close to where people work. Good planning can prevent low-cost housing areas becoming ghettos, or being placed where there are no services.

Housing is difficult to plan for and for governments to invest in for many reasons. It's expensive, so difficult choices have to be made. Planning across multiple areas of infrastructure is complex, and vested interests can make it more difficult.

Local and central government can each blame the other, as we've seen in Auckland. We do not have good enough data on how many people are in need, where and who they are, or what their other needs are.

However this should not stop us from investing in social housing. There is no question that homelessness is now a crisis in New Zealand, particularly in Auckland. It affects the poor and it affects children.

The time for hand-wringing, obfuscation and blaming others is over. We expect more from our leaders and we need a plan to invest in social housing. It should be planned as a part of New Zealand's core infrastructure.

The cost will be high, but where we choose to invest says a lot about the society we are. Are we prepared to have children sleeping in cars and garages or will we invest in their future?