The "Children of the Recession" study showed that the number of minors living in poverty in 41 countries had swollen to 76.5 million since the deepest crisis since the Great Depression took hold.
"Many affluent countries have suffered a 'great leap backwards' in terms of household income, and the impact on children will have long-lasting repercussions for them and their communities," said Jeffrey O'Malley, Unicef's head of global policy and strategy.
The study by the United Nations' children's aid agency assessed members of the Organization for Economic Cooperation and Development grouping of industrialized nations, as well as European Union countries.
It found that in 23 of the 41 countries, child poverty had risen as a direct result of the crisis.
Children were particularly hard-hit in nations that have suffered the most.
In Ireland, Croatia, Latvia, Greece and Iceland, poverty rates rose by over 50 percent.
In Greece, the most symbolic of all Europe's crisis casualties, median household incomes for families with children had sunk to the 1998 level — the equivalent of receding 14 years on the income ladder.
Those in Ireland and Spain lost a decade, as did Luxembourg, even though it remains among the wealthiest economies in Europe.
Families with children in Iceland lost nine years, while Italy, Hungary and Portugal lost eight.
Underlining the impact of the crisis, Unicef said the percentage of households unable to buy meat, chicken or fish every two days had more than doubled in countries such as Estonia, Greece and Italy.
It said while early stimulus programmes in some countries were effective in shielding children, by 2010 the bulk of countries had pivoted to budget cuts.
The negative impact on children was particularly potent in the Mediterranean region, it said.
Sweeping budget cuts in social safety nets had a serious knock-on effect, Unicef said.
Social safety nets crucial
"Unicef research shows that the strength of social protection policies was a decisive factor in poverty prevention," said O'Malley.
"All countries need strong social safety nets to protect children in bad times and in good — and wealthy countries should lead by example, explicitly committing to eradicate child poverty, developing policies to offset economic downturns, and making child well-being a top priority," he added.
In the United States, where extreme child poverty has risen more in this slump than during the recession of 1982, social safety nets provided key support to poor working families but were less effective for the jobless ultra-poor, Unicef said.
Child poverty has increased in 34 out of 50 US states since the start of the crisis.
In 2012, 24.2 million children were living in poverty, a net increase of 1.7 million from 2008, the study showed.
There was some good news, however.
In 18 countries, including Switzerland, child poverty actually fell, sometimes markedly.
Australia, Chile, Finland, Norway, Poland and Slovakia, for example, reduced levels by around 30 percent.
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