"Social investment'' seeks to help the "vulnerable'' by intervening early in their lives, and it cuts across several areas of government spending.
Methodist Mission Southern director Laura Black said the Budget was about putting the "machinery'' in place for the as-yet unknown replacement for the Child Youth and Family service.
The wider social sector also faces changes because it needs to fit the "social investment'' approach, but the detail remains unknown.
Ms Black said it was not clear how the $43 million set aside for children most at risk of not achieving would be managed.
"How's the school going to allocate that in a way that makes a difference for that child ... what's the mechanism?
"I suspect this is a trial at rejigging the decile system, and it will be interesting to see how the Government's logic model will work.''
For low-income people, the Government's apparent lack of ideas for tackling the Auckland housing crisis was a major problem.
"People who are trying to live in the one place with really big job growth can't afford to be there, and there doesn't seem to be an answer for that.''
Social Development Minister Anne Tolley said the overhaul of the child protection system would be delivered by March 2017.
"Budget 2016 allows us to begin the radical overhaul which our care and protection system needs, for the sake of young New Zealanders.
"We must always look at new ways of supporting at-risk people to gain employment and to improve their lives,'' Mrs Tolley said.
Social investment
• $652 million for social investment package.
• Includes $348 million to develop new child protection scheme.
• Spans multiple government departments.
• Extra funding for Youth Service (youth employment), Whanau Ora, education, welfare dependence initiatives, and prisoner reintegration.
