Government Minister Grant Robertson has revealed 16 children are living in homes where a parent has had their benefit slashed after failing a drug test.
Nearly 40,000 beneficiaries were sent for jobs that required a drug test last year, with 114 failed results.
Seventy-two beneficiaries were sanctioned and had their benefits cut - those with children have their benefit cut in half.
On Thursday, National's social development spokesperson Louise Upston asked the Government how many households with children were affected.
"I believe in the last year the number is nine (households) with 16 children involved," Mr Robertson replied on behalf of the Social Development Minister.
In Opposition, Mr Robertson's colleagues opposed the drug sanctions that National introduced in 2013, warning that slashing parents' benefits would severely damage children.
"Does (the Minister) agree with the statement, 'drug sanctions have a negative impact on the unemployed', if so why is (the Minister) not removing the sanction for failing to pass a drug test?" Ms Upston asked.
"Sanctions are part of a picture for the Government but they are a last resort, as they should be," Mr Robertson told Parliament.
"On this side of the House we believe there are a range of ways of making sure that people look after their children and their family by supporting those families into training and into work and by getting them into medical facilities."
Nearly two-thirds of the beneficiaries who failed a drug test last year were sanctioned.
On Wednesday, Ms Upston asked the Social Development Minister Carmel Sepuloni during Question Time: "Does she have an expectation that those employed in her office do not come to work under the influence of drugs and, if yes, what's the difference between that and the expectations on those receiving a taxpayer funded benefit?".
Ms Sepuloni responded: "I absolutely have that expectation."
However, unlike beneficiaries, politicians and their staff are not required to undergo state-monitored drug testing.
Further, unlike beneficiaries, there are no legislated sanctions in place to punish politicians or their staff if they fail or refuse a drug test.
Children's Commissioner, Judge Andrew Becroft, told 1 NEWS last week that the policy is unjust.
"Children shouldn't be penalised for the actions of adults over which children have no control - I think it is unprincipled and as Children's Commissioner I would be derelict in my duty if I didn't say please reconsider," Judge Becroft said.