In this week's debate, Bernie Sanders claimed that the United States has the highest rate of childhood poverty. CBS reports that Sanders said: "We should not be the country that has the highest rate of childhood poverty of any major country and more wealth and income inequality than any other country,"
As even CBS notes, according to UNICEF, which is probably the source of Sanders's factoid, the US has lower childhood poverty rates than Greece, Spain, Mexico, Latvia, and Israel, all of which are OECD countries or regarded as peer countries. The US rate (32.2 percent) is also more or less equal to the rate in Turkey, Romania, Lithuania, and Iceland. See page 8 of this report.
So, while Sanders probably doesn't even know what he means by "major country" it's clear that the US is not an outlier among OECD-type countries, even by UNICEF's own analysis.
We get much more insight, though, once we have a look at what UNICEF means by "poverty rate." In this case, UNICEF (and many other organizations) measure the poverty rate as a percentage of the national median household income. UNICEF uses 60% of median as the cut off. So, if you're in Portugal, and your household earns under 60% of the median income in Portugal, you are poor. If you are in the US and you earn under 60% of the US median income, then you are also poor.
The problem here, of course, is that median household incomes — and what they can buy — differs greatly between the US and Portugal. In relation to the cost of living, the median income in the US is much higher than the median income in much of Europe. So, even someone who earns under 60% of the median income in the US will, in many cases, have higher income than someone who earns the median income in, say, Portugal.
Here are all the median incomes (according to the OECD's household income comparison statistic called "median disposable income.") When adjusted for purchasing power parity, the statistic allows us to make incomes comparable across countries that use different currencies and have different costs of living. This takes into account taxes, and social benefits paid to households. So, let's use it to compare (the Y axis is in "international dollars"):