Major changes to the benefits system coming into force on Thursday will condemn hundreds of thousands more children to poverty, charities have warned.
The Children's Society called on the Government to think again over imposing a new "two-child limit" on Universal Credit and child tax credit as the move will impact on three million children.
The Joseph Rowntree Foundation (JRF) made a similar plea as it cited independent research forecasting that 200,000 children may be pushed into poverty by the changes.
The Children's Society calculates that a nurse with three children, earning £23,000 a year, who becomes a single parent stands to lose £2,780 a year if he or she makes a claim for tax credits or universal credit under the move.
The charity's chief executive Matthew Reed said: "Children shouldn't have to worry if there's enough food to feed the family tonight, or whether to tell their mum that their school shoes don't fit any more. But this week's child tax credit cuts will condemn hundreds of thousands more children to lives overshadowed by poverty.
"Children will be losing thousands of pounds a year in support that should be helping them to lead happy, healthy lives. This means more children at risk of illness, poor school results and mental health problems.
"At a time when child poverty is already on the rise, the Government should not be pressing ahead with these cuts. We urge the Prime Minster to reconsider these changes and weigh the devastating impact they will have against her pledge to help struggling families."
JRF's Katie Schmuecker also called on Ministers to reverse limiting payments to the first two children.
"Universal Credit remains the right thing to do. The current system is fragmented and traps people in poverty and the prospect of an integrated benefit system that responds to people's changing circumstances is a prize worth having.
"But some changes introduced this month are forecast to increase poverty. This will cost us all dear: an estimated £1 in every £5 spent on public services is linked to dealing with the impacts of poverty.
"For children, growing up in poverty scars their prospects and reduces future earnings, costing the Treasury £6.4 billion a year in lost tax revenue and additional benefit spending."