"Programmes that are targeted to the poor tend to end up being poor programmes," he said.
Members of an expert group on child poverty appointed by Children's Commissioner Dr Russell Wills also defended their proposed universal payment for young children at the workshop, part of a seven-week consultation on the group's initial report which ends on October 12.
Mr Key described the proposal as "dopey" when the report was released on August 12. He said the current family tax credits gave more support to poorer families, reducing gradually as family incomes rose.
Victoria University's Professor Jonathan Boston, who co-chairs the expert group, said a shift to a high universal payment for young children, combined with lower targeted payments for older children, would have advantages.
Socially, it would encourage one parent to stay home to look after very young children. Modelling in the group's report suggests universal payments of $8000 ($154 a week) in the first year, $7000 ($135 a week) in the second year and $6000 ($115 a week) in the third year, then lower income-tested payments stepping down at ages 3, 5 and 14.
"One of the arguments for a universal child payment of a generous nature is to recognise the enormous importance of the mother in this case being with the child, particularly during the first year," Dr Boston said.
"From a society's point of view, all children matter, and we as a society should be taking responsibility to ensure the best possible outcome for our children."
The group argues that a universal payment would be fairer than extending paid parental leave.
A bill to extend paid leave to six months, sponsored by Labour MP Sue Moroney, was given a first reading in Parliament by a one-vote margin in July and is before a select committee.
"All infants would benefit and not merely those whose mother was eligible for paid parental leave," the group said.
Professor Boston said a universal payment would give parents bigger incentives to get paid employment when their children were old enough.
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