About 1.6m children in the UK are living in severe poverty, Save the Children says.
The charity, which found the highest levels of child poverty in Manchester and Tower Hamlets, in London, said the figure was a "national scandal".
And it said more children would be tipped into poverty by public sector job losses and changes to benefits.
The government said it was "fully committed to the goal of eradicating child poverty by 2020".
Of the UK nations, Save the Children found Wales had the highest proportion of children living in severe poverty (14%), followed by England (13%) then Scotland and Northern Ireland (9% each).
It found 29 authorities across the UK had more than one in five children living in severe poverty.
Manchester and the London borough of Tower Hamlets had the highest rates of children living in severe poverty at 27%.
The London borough of Newham had 25% in severe poverty, Leicester and Westminster (London) had 24%, Nottingham, Liverpool and Birmingham 23% and Blackpool and Hackney (London) 22%.
In Wales, the local authority with the highest rate of severe child poverty was Blaenau Gwent at 20%.
In Scotland, Glasgow City had the highest rate of child poverty with 18% living in severe poverty.
The charity based its regional breakdown of child poverty on statistics from the New Policy Institute.
It defines severe poverty as those living in households with incomes of less than 50% of the UK median income (disregarding housing costs).
'Born without a chance'
Sally Copley, Save the Children's head of UK policy, said: "Children up and down the country are going to sleep at night in homes with no heating, without eating a proper meal and without proper school uniforms to put on in the morning.
"No child should be born without a chance. It is a national scandal that 1.6 million children are growing up in severe poverty.
"If these children are to have a future, we must acknowledge their desperate need and urgently target government help towards them."
A spokesman for the Department of Work and Pensions said: "Over the last decade vast sums of money has been poured into the benefits system in an attempt to address poverty, this approach has failed.
"Our radical welfare reforms will benefit the poorest in society, helping 350,000 children out of poverty, and targeting support at those who need it most to make work pay and break the benefits trap.
"We know that work is the best route out of poverty."