As the second round of welfare reforms come back before Parliament, Social Development Minister Paula Bennett says the 650 children born to women already claiming a benefit in January are reason enough for her tough reforms.

The Social Security (Benefit Categories and Work Focus) Amendment Bill will have its second reading in Parliament this afternoon.

The Government has been slammed for cracking down on youth and sole-parent beneficiaries when the unemployment rate is soaring because there aren't enough jobs.

Opponents argue that rather than picking on the vulnerable, the Government should focus on boosting the economy.

But Bennett is unapologetic about the welfare reforms, which are midway through implementation.

And she said the focus on sole mothers and young people was deliberate.

There were 659 subsequent children born to parents already claiming a benefit this January, she said.

Under changes introduced last October, those mothers will have to return to work when that child is 12 months old, if their older children are aged over five.

Bennett said Work and Income staff used discretion to excuse 22 of those parents from the work requirement, largely because of timing around the announcement and implementation of the policy.

Meanwhile, in 2010 more than 7.5 per cent of live births - 4800 of 63,900 - were babies born to solo parents on the Domestic Purposes Benefit (DPB) and Emergency Maintenance Allowance.

And between 1993 and 2011, 29 per cent of solo mothers on the DPB had another child.

"It does tell us that those that are already on benefits with children are still having subsequent children," Bennett said.

"The effects of them potentially being longer on [a] benefit are what have led us to make this sort of policy change."

The minister has long-highlighted research which shows children in low income households, like those relying on a benefit, have poorer health, education and social outcomes.

Bennett admits work-testing for sole parents was among the "tougher" reforms.

But in 10 months of last year there were fewer people going on to the DPB than coming off, a feat which has only been achieved twice in the last 16 years - once when Working for Families was introduced.

"That, in these sorts of times, is remarkable really," Bennett said.

"That's when we really start talking to mums in particular - 90 per cent of them are mums - about what they're going to do, that their child's going to be turning five soon."

Critics say the reforms are too punitive - cutting benefit payments when parents don't meet certain criteria - but Bennett says the real impact is coming not from the requirements to get a job, but from the work preparation being done with beneficiaries.

"People will hide behind keyboards and bag you on a blog," she said.

"I also hope, and think, that people who need state support and are on welfare, they're seeing that it's not near as punitive and not near as nasty as my opponents were making it out to be."

Green Party co-leader Metiria Turei said sole parents and their children were being demonised by the reforms.

"Welfare reforms that punish these women for having children are a complete distraction from Government's failure to provide jobs," she said.

Labour's social development spokesman Jacinda Ardern said she got many letters from sole parents who were struggling to find work.

"This set of reforms will do absolutely nothing to improve their job prospects through either training or education, or by addressing the underlying issues of the inavailability of work, particularly work that suits their childcare needs."

The reforms did little more than respond to rhetoric, she said.