The Children's Society's speaking as Parliament debates the government's Welfare Reform and Work Bill today.
Part of the bill includes freezing Child Tax Credits, Working Tax Credits and Job Seekers' Allowance for the next four years, rather than raising them in line with inflation.
The charity has also said 4.9 million children - two-thirds of those who could be affected - live in households where one or both parents work. Those households receive benefits to top-up low pay.
It's urging MPs to reconsider and stop the benefit freeze, as well as other spending cuts which will affect low-income families.
Sam Royston, Children's Society Director of Policy, told Premier: "This is going to have still further impacts on that group of families who've already been sorely affected by some of the measures up to today.
"That's going to put real pressure on families who're already struggling to make ends meet, making it much harder to put food on the table and to heat their homes.
"That's why it's so important that when this bill is debated the government reconsiders this four-year freeze on benefits like child benefit, like child tax credit."
A DWP Spokesman said: "The reality is that our welfare reforms are incentivising work while protecting the most vulnerable, and ensuring we have a system which is fair to those who pay for it, and to those who benefit from it.
"We are bringing welfare spending under control, while - crucially - helping people into work, and through Universal Credit helping them to earn more.
"More people than ever before are now work, wages are rising above inflation, and the National Living Wage is set to boost pay even further."
Listen to Premier's Alex Williams speaking to Sam Royston:
