More than 40,000 single parents - most of them women - have lost cash after a £500-a-week limit was placed on welfare payments received by workless households.
It means 56% of families losing out are single parents - more than the 50% predicted by the Government when the measure was introduced in April 2013.
And 22,000 of those families had a child under four years of age, the Department for Work and Pensions statistics reveal.
They were released ahead of the lowering of the benefit cap from £26,000 a year to £23,000 in London - and just £20,000 in the rest of the country - from autumn this year.
That move has already alarmed Gingerbread, a charity working with lone parents, which has warned it will both cause suffering and fail to get more people into work.
Fiona Weir, Gingerbread’s chief executive, said: “Single parents and their children will continue to bear the brunt of this cut, losing even more support when many are already struggling to get by.
“Despite government claims the cap helps people into work, most people affected so far haven’t been able to do so.
“It can be extremely difficult for single parents with very young children to find a job they can balance with caring for their child, not to mention the money needed to pay nursery fees.”
In total, 73,000 households have had their benefits cut - the majority by up to £50 or 10% of their income.
Around 25,000 families have had a cut of up to £150 and 156 households across the country have lost £400 or more.
Most were in London but there were 13 in Luton, 6 in Bristol, 7 in Edinburgh and 5 in Dundee.
The benefits cap limits the weekly support to £500 for a couple, with or without children, and single parents. For individuals without a child it is £350.