The End Child Poverty coalition said the problem was worst in large cities, especially London, Birmingham and Manchester.
The coalition of charities, faith groups and unions warned that low income families will find it increasingly difficult to pay for basic essentials in the coming years as prices rise while benefits are frozen.
There are more than three and a half million children living in poverty, ranging from one in 10 in some areas to 47% in others, said the report.
A study of Parliamentary constituencies showed those with the highest levels of child poverty included Birmingham Ladywood, Manchester Central and Poplar and Limehouse in London, while those with the lowest included Gordon, West Aberdeenshire and Kincardine, Sheffield Hallam and York Outer.
End Child Poverty chairman Sam Royston said: "As the Prime Minister has rightly recognised, this is not a country that works for everyone. In every community, there are children being denied the happy childhoods and the good start in life other children take for granted. Our children are now twice as likely to be poor as our pensioners.
"Many families who are just about managing today, won't be managing tomorrow if Universal Credit leaves them with fewer pounds in their pocket, and if rising costs of living means their money doesn't stretch as far as it used to.
"This month's Autumn Statement is a major opportunity for the new Government to act to help these families.
"We urge the Chancellor to reverse the significant cuts to Universal Credit targeted at working families and, at the very least, shield children's benefits from inflation."
The coalition's figures calculate that households are living in poverty if their income (adjusted to account for household size,) is less than 60% of the average. All poverty rates are calculated on an after housing costs basis.
Margaret Greenwood, shadow minister for employment and inequalities, said the report was shocking.
"Over half of those living in poverty are in working households. It's clear that low pay, insecure work and the lack of affordable housing are taking their toll on UK families and the children of this country are suffering as a result.
"That's why Labour is calling for the full reversal of damaging cuts to Universal Credit which will leave 2.5 million working families on average £2,100 worse off."