"The focus should be on getting them skills and getting them jobs...this is really a nanny state (policy)."
Mr Goff said if the argument was that young people couldn't manage their budgets, the same thing could perhaps be said of someone who was 37.
"This shouldn't be about politics, this should be about making sure that our school-leavers have a proper transition from school to work," he said.
Mr Key, speaking at his post-cabinet press conference, said 90 per cent of the young people targeted by the new policy were destined to go on the adult benefit when they reached 18.
"That's why we're going to intervene to get them back on track," he said.
"We need somebody walking alongside them, a wrap-around service. They're disengaged from education, work and training, many of them they haven't had an adult in their lives for a long time and they're often raising a child."
Mr Key said many of the young girls who were on benefits were raising babies and they were preyed on by young males who used them as a source of income.
"A young person bringing up a child has a responsibility to make sure that child is fed, housed and warm," he said.
"I'm not going to make an apology, to anybody, for ensuring that happens...I don't care if that offends a few people. What I care about is those kids and this is going to make sure they do have a house, warmth and food."
Mr Key said about a third of the payments to the caregiver adults who were assigned to the young people would be a bonus linked to outcomes like getting their charges into training so they didn't go on a benefit at 18.
He said similar systems were operating in European and Scandinavian countries, although none was identical, and they seemed to work well.
Speaking about welfare generally and the Government's intention to complete an overhaul before the election, he said there was no specific target on numbers.
"I think we can get to a welfare system where there are clearer obligations on both parties. I think we can get to one that is more effective, with better outcomes," he said.
- NZPA