Record levels of poverty in working families
More than two-thirds of the children living in poverty in the UK are in families where at least one parent is working, according to official figures.
This is more than ever before in statistics going back 20 years - up from 43% in 1996-97 to the current 67%.
There are now four million children in poverty, the highest since the 2008 financial crash.
The Child Poverty Action Group said it showed families were "stuck on low pay while living costs rise".
The figures on low-income households show that in-work poverty has become the most common form of child poverty.
The Child Poverty Action Group, highlighting the prime minister's pledge to support "just about managing" families, said the government needed to act urgently to tackle the "burning injustice" of child poverty.
And the Children's Society described the figures as "truly shocking".
But the Department for Work and Pensions said that work still paid - and that children were five times more likely to be in a low income family if they lived in a workless household, rather than a "household where all adults work".
The figures show that the biggest increases in earnings have been among the highest earners - and the lowest increases have been among low earners.
This has helped to push up the overall average household income to a record level of £481 per week.
But the study defines "relative low income" as earning less than 60% of the most typical median income, which for a combined household income stands at below £25,100 per year.
The profile of low income also shows how thresholds for poverty can change between different types of households.
To be in the bottom 10% in terms of living standards, a single person would have an income below £8,500, while for a couple with two young children the figure would be £17,800.
There are also big regional variations when housing costs are included.
London has the highest rate of child poverty when housing costs are added.
But if accommodation is excluded, the West Midlands and Northern Ireland have the highest proportion of child poverty.
The figures on child poverty and employment are significantly different for couples and lone parents - with much higher levels of work among couples.
Among couples with children in poverty, the proportion without one of these parents working is only 13%.
But for children in poverty living in a lone parent family, only 12% of parents are in either full-time or part-time work.
The figures also consider poverty in terms of "material deprivation" for children - measuring access to a list of goods and services - and this has remained broadly similar over the past five years.
"These figures are grim, but, according to independent experts at the Institute for Fiscal Studies, the outlook for the next few years is bleaker," said Alison Garnham, chief executive of the Child Poverty Action Group.
"Most worrying of all is that the government seems to be in a state of denial. Last week's Budget failed to mention poverty even once."
Anne Longfield, Children's Commissioner for England, said: "These very troubling figures show tackling child poverty is more important than ever.
"Behind every statistic is a child living a life in poverty, with all the negative consequences that can have for their health and their future life chances."
Justin Watson, head of Oxfam's UK Programme, said the figures on poverty were "deeply worrying".
"There are now more people in poverty in the UK than there have been for almost 20 years and a million more than at the beginning of the decade," he said.
But a Department for Work and Pensions spokeswoman said: "Average household incomes have risen to a record high and income inequality is lower than in 2009-10.
"Today's figures confirm that work is the best route out of poverty, so it represents significant progress that the number of children living in a workless household is down by 590,000 since 2010.
"We have introduced Universal Credit, the National Living Wage and increased the tax free Personal Allowance to make sure it always pays to be in work.
"But one child living in poverty is one too many and we remain committed to tackling the root causes of disadvantage."