Child poverty charities warn that the Government's response to the cost of living crisis risks reversing the fall in the number of children living below the breadline across the UK.
Department for Work and Pensions data shows 28,029 children aged under 16 were living in families with low incomes in 2020-21 – an estimated 26.4 per cent of all youngsters in the area.
That was up from 25.9 per cent the year before, and the highest since comparable records began in 2014-15 – when the figure stood at 19.4 per cent.
A family is defined as in low income if it earns less than 60 per cent of the national median household income before housing costs are considered.
Families are included in the figures if they have claimed child benefit alongside another means of support, such as Universal Credit, tax credits or housing benefit, at some point in the year.
Different figures – which take housing costs into account – show 3.9 million UK children were living in relative poverty in 2020-21.
This was down from 4.3 million the year before, but still above the 3.6 million in 2010-11 – a decade previously.
The Child Poverty Action Group said this fall shows the UK Government has the power to protect children from poverty.
But Alison Garnham, chief executive of the charity, said: "Many of the children who were lifted out of poverty by the £20 increase to Universal Credit have already been forced back over the brink by the Government’s actions.
"And as millions struggle with spiralling costs, we know the picture will worsen."
Of the children aged 0-15 in poverty in Sheffield last year, 8,360 (30 per cent) were aged below five.
There were also 6,185 young people aged 16-19 in low income families.
Meanwhile, the majority of youngsters aged 0-19, 59 per cent, were in working households.
Action for Children said the Government risks failing on its manifesto pledge to cut child poverty and force millions of families into years of "miserable hardship" without further measures.
Imran Hussain, director of policy and campaigns at the organisation, said: "As prices continue to rise, more low-income parents who were just about managing could go under, with no tips, tricks or hacks left to stretch their income over the month.
"As well as the current cost of living crisis, many families with children are still reeling from October’s £20-a-week cut to Universal Credit."
The Department for Work and Pensions said the data should be treated with caution, especially when compared with previous years, due to changes in data collection during lockdowns, which affected the sample size and composition.
A Government spokesman said the landscape is different now than it was during the pandemic and that filling the record number of vacancies is the best route out of poverty.
He added that UC changes mean claimants in some working households are £1,000 better off on average, that the minimum wage is rising to £9.50 from April 1 and National Insurance will be cut for more than 30 million people from July.