The study also found that British children are worse off than children in Poland and Romania.
The charity, Church Action on Poverty, says that although unemployment is on the decline and the economy is growing, the cost of living is outstripping wages - particularly for the poor - and benefit cuts mean the poor are relying more and more on foodbanks.
The United Kingdom is the world's sixth-largest economy, but it ranked only 25th out of 41 developed countries in the world for child poverty in Unicef's report.
Liam Purcell,Church Action on Poverty's communications and supporter relations manager, told Premier's New Hour: "We've got a sanctions regime on benefits, which is making more and more people completely destitute, often very unfairly, so we've now got millions of people relying on foodbanks.
"The austerity regime that we've seen and the impact of recession; everything has hit the poorest and most vulnerable hardest.
"We need a positive vision that talks about rebuilding the social safety net, making sure nobody is left to go destitute in the sixth-richest country in the world.
"Church leaders are really stepping up. They're fulfilling the Church's mission of being on the side of the most vulnerable and excluded. They've been speaking out about the problems they see and really being a prophetic voice.
"All of the UK's denominations now guarantee a living wage to all their staff, and just last month the Church of England announced that every Church of England school is now going to be paying a living wage to all its staff."
In a statement to The Independent, the Department for Work and Pensions suggested the Unicef figures could be distorted.
A spokesperson said: "Unicef is drawing distorted comparisons with this data.
"ONS figures show that under this Government, around 300,000 fewer children are in poverty or growing up in workless families.
"Our reforms are improving the lives of some of the poorest families by promoting work and helping people to lift themselves out of poverty."