Budget papers show the Government considered making solo parents return to full time work when their youngest child was 12, instead of 14, but decided against it.
The papers also show it was former Social Development Minister Paula Bennett's idea to require solo parents to re-apply for their benefits every year "to send a strong message that benefit receipt is expected to be temporary."
The Ministry of Social Development also advised that change would come at a cost of between $8 million and $11.5 million over four years to administer.
The papers show the Government started work on the centrepiece of its Budget last August - a month before the election.
That was a $790 million 'child hardship' package aimed at low income families.