Single parents would be "helped" back to work sooner under tough new plans unveiled by the Liberal Democrats.
Lone parents can claim benefit until their youngest child is 16
Lone parents can currently claim income support until their youngest child is 16, but the Lib Dems propose to bring the age limit down in stages.
At first, benefit would end when the
youngest child starts secondary school.
The plan, which could cut up to £2bn a year from the benefits bill, was unveiled by work and pensions spokesman David Laws.
Mr Laws said the move was vital to tackle unacceptable levels of child poverty, and denied it marked a shift to the right.
The party's spring conference in Harrogate - the first under its new leader Sir Menzies Campbell - has already seen members back the part-privatisation of the Royal Mail.
'Out of kilter'
In a speech to the conference Mr Laws said: "Our benefit rules are totally out of kilter with every other developed country.
"There is no obligation to be in employment until your youngest child turns 16. You can remain on income support from the birth of your eldest until your youngest turns 16.
"You could be out of the labour market for quarter of a century."
"We need to give parents additional opportunities, and responsibilities, by helping them back into work," Mr Laws said.
He said families had responsibilities to "try to look after themselves and their families and not rely on the benefits system for 20 years".
Denying the plan suggested a move to the right, he said it had to be viewed alongside other policies, such as more generous pensions.
"To deliver social justice we will need economic dynamism and economic discipline," he said.
"We need to show how we can create wealth as well as redistribute it and make tough choices and not just the easy ones."