Liberal Democrat Danny Alexander has accused the Conservatives of being bent on "slashing support for families" while the two parties were in coalition.
Alexander said £8 billion of proposed welfare cuts that the Lib Dems blocked included limiting Child Benefit and Child Tax Credit to two children at a cost of £3,500 for a family of three.
The Tories said they did not recognise the figures cited and called the claim "desperate stuff".
Conservative leader David Cameron has ruled out any changes to child benefit, after accusations the Tories are secretly planning to make cuts after the election.
Speaking to ITV News deputy political editor Chris Ship, Mr Cameron said there was a two-year freeze on the payment, which he labelled an "absolutely crucial" benefit.
And pushed on the subject, he confirmed there would be no change to the current arrangement at all - neither in terms of the higher rate nor in terms of means testing.
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.