So important is this obligation that Article 3 cannot be derogated from by any state party to the Convention. Further, the obligation is considered a part of customary international law. It is at the core of any decision-making touching on children, whether directly or indirectly.
This obligation mandates a child-centred approach to policy decisions and their implementation. It requires politicians and others, including civil servants, to actively consider and determine what is in a child's best interests, not simply take it for granted.
Yet, the Amnesty International reporting shows that we are not taking this obligation seriously in New Zealand. There is no active guarantee that policy decisions are made in the best interests of children.
At Child Poverty Action Group we have consistently worked to highlight where our policy choices fail children.
We are concerned that in this country our paediatricians see third world diseases. We are concerned that in this country our homes are so low in quality that our children suffer while landlords benefit.
Ultimately, we are concerned that the obligation enshrined in international law as being so fundamental that it cannot be derogated from, that the child's best interests be a primary consideration in law and policy, is an obligation that in this country we fail to properly secure.
An example is the operation of the Working for Families scheme. This scheme is aimed at supporting families by providing an adequate income to enable children to thrive. Yet, the operation of the scheme directly fails to take account of the best interests of those children it is supposed to be supporting.
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Worse, the operation of Working for Families chooses to discriminate against one group of children, through no fault of their own. Those children whose parents do not meet a work threshold lose out on $72.50 a week through being denied the "In Work Tax Credit".
In truth, it is those children who, more than others, need that $72.50 a week. That money buys a lot of food, school uniforms, and medicine. And, beyond the rhetoric, the research shows that more money in the hand goes straight to helping children.
To deny that support to those children, which is available to other similarly placed children, is clearly contrary to their best interests and is discriminatory.
The In Work Tax Credit fails children and is a policy that cannot be justified on any child-centred approach. Further, its operation is so complicated and ultimately punitive in that its costs - both fiscal and social - outweigh any supposed benefits.
For these reasons, Child Poverty Action Group calls on this government to fulfil the best interests of our children. A simple and immediate step would be to extend the In Work Tax Credit and Fix Working for Families. Overnight, this would make a huge and powerful difference to the lives of thousands of children and is consistent with the government's stated commitment to responding to child poverty.
At our website we set out more the basis around which we say the government can Fix Working for Families. We can do this in a way that is fairer, affordable, and, ultimately, in our children's best interests.
No one can deny that our children deserve more opportunities and the best possible start to life. The downstream benefits are huge - better health, education and employment outcomes. Our society benefits when our children's best interests are fulfilled.
We do a good job of looking after our elderly and seem content, as a society, to meet those fiscal costs across the board, but why do we fail our children and not do the same for them?
Michael Timmins is a member of the Child Poverty Action Group management committee.