The union organisation claimed that the impact of Government policies, coupled with slow wage growth, will mean that hundreds of thousands more children will be living below the minimum income standard by 2015.
Half a million more children will be pushed below the breadline in the next few years under the Government's tax and welfare reforms, the TUC has claimed.
The TUC, which based its analysis on a minimum income standard of just under £24,000 a year for a single parent with two children and £24,600 for a couple with one child, said that just over half of all children in the UK will be living below the standard in two years' time.
Tax and welfare changes, including tax credit cuts, and the VAT rise to 20% will have the biggest impact, compounded by wage freezes in the public sector, said the report.
TUC general secretary Frances O'Grady said: "Families are suffering the tightest squeeze in their living standards in nearly a century. On top of wages that do not keep up with prices, Government policies are making life even more miserable for millions of low to middle-income families through tax increases and cuts in benefits and tax credits.
"By the 2015 election, the majority of children in Britain will be living below the breadline. For any civilised society, that should be shaming.
"But while the Prime Minister says there is no alternative, the truth is that support is growing for a new approach. The Budget should start from recognising that what Britain faces is a growth, jobs and living standards crisis. Rather than targeting tax cuts at millionaires, cutting VAT would benefit everyone, and would help poorer households far more than raising the personal allowance."
The report was published ahead of a TUC-organised pre-Budget rally in London.
David Holmes, chief executive of Family Action, said: "Children are paying too high a price in the Government's battle to reduce spending. We know that family income is the biggest influence on a child's outcomes in education, health and behaviour.
"With the Budget looming, we urge the Chancellor to think again about the impact of his welfare and early intervention cuts on the life chances of children and young people."