"But where does the $21 million come from? Something has to give and she needs to tell us if she's cutting other services or provider funding."
She also questioned the timing, given it was close to an election and Ms Bennett had requested submissions on a Green Paper on Vulnerable Children to inform future policy.
Ms Bennett said one example of savings was $8 million a year the department had saved from choosing a preferred provider for medical alarms.
She said the increase in social workers would happen over a few years - it was expected to cost $5 million in the first year when the priority would be getting at least 40 more of the CYF social workers in place. She had been concerned for some time about the capacity of CYF to cope with increased calls on its current staff levels. It now received about 150,000 notifications of abuse each year - almost four times more than in 2006.
"They are often complex cases and as a consequence we are putting a lot more resources into the front line."
Schools had also asked for more social workers.
"Every principal and teacher I have spoken to says these social workers are pivotal in dealing with what are sometimes quite complex issues with our children."
She expected many of the new social workers would be people returning to the workforce or new graduates, who would work with supervision.
Robin Duff, president of the Post Primary Teachers' Association, said the measure was commendable, but ignored secondary schools which was where problems first arose.
"Violence at home is directly linked to challenging behaviour in schools. It's positive to tackle the problem at primary level but the early life of the problem often starts at secondary school."
He said secondary schools were heavily dependent on the police to help them.
The policy:
* 149 more social workers in primary schools
* extend Social Workers in Schools to all 673 decile one to three schools - 388 more than now. Cost: $11.1 million more a year
* 96 more social workers for Child Youth and Family's child abuse team - a 10 per cent increase. Cost: $10.3 million a year.
* Will be phased in over a few years. Expected cost in first year: $5 million.