Under the Tory government, the country has seen an almost 20% increase in its child income poverty rate, ranking last place in Unicef's league table for reducing child poverty.
Iceland was the next worse but with a significantly lower rise of 11%, while France had a 10.4% rise.
At the opposite end of the scale, Poland topped the list with a 37.6% cut in its child poverty rate, followed by Slovenia with a 31.4% reduction rate.
Comment: Here's the chart with all nations for comparison; at the bottom of the chart, after Norway, it's: Switzerland, France, Iceland, and last is the UK:
The report - titled Child Poverty in the Midst of Wealth - compared relative income with poverty rates, which means the proportion of people who fall below a threshold relative to the income of the average person in the population.
The change in child income poverty was measured over a seven-year period, comparing poverty rates in 2012-14 with 2019-21.
Comment: And even in just the last 2 years, since those measurements, other metrics reveal that the situation has gotten considerably worse.
Unicef compared the average poverty rate over a three-year period owing to difficulties collecting data during the pandemic.
In a separate table when measured on its most recent poverty rate, which was 20.7% of children being in poverty in the period 2019-21, the UK ranked 28th out of 39.
It means the country's overall ranking, which combined the two measurements, was 37th out of 39 - behind Colombia and Turkey.
The findings come from Unicef's Report Card series, which analyses date on children's wellbeing.
Chief executive of the United Kingdom Committee for Unicef Jon Sparkes said: "We urge the UK Government to take steps to protect all children from poverty, starting by making child poverty reduction a government priority, scrapping the two-child limit policy and benefits cap, and improving services and support, especially for the youngest children."
Commenting, the SNP's Kirsten Oswald MP said: "This report lays bare the damaging impact of 13 years of Tory rule. Consecutive Westminster governments, which Scotland didn't vote for, have repeatedly prioritised austerity and support for the rich over efforts to tackle rising rates of child poverty and support families, showing exactly why Scotland needs independence.
"And what's worrying is that Sir Keir Starmer has confirmed a Labour government would continue down the same path. Labour have signed up to Tory tax and spending plans and austerity, including keeping the poverty-inducing two-child cap that is impacting over 87,000 children in Scotland."
The latest figures come after statistics released by the End Child Poverty Coalition found almost 90,000 Scottish children were being hit by the two-child cap in the lead-up to Christmas.
Speaking to The National, the SNP's social justice spokesperson David Linden (below) said: "It is a matter of urgency that the poverty-inducing two child cap is abolished - that is why I am urging the UK government to abolish it without delay. Doing so could lift 250,000 children - 15,000 in Scotland - out of poverty.
"The goal to reduce, and eventually eradicate, child poverty will need the efforts and voices from across the political spectrum. That is why I am also urging Sir Keir Starmer to reverse his decision to keep the cruel policy under a Labour government and join us in putting pressure on the Tory government to scrap it.
"If he will not then he is making clear, once again, that Labour's values do not align with Scotland's values, including lifting children and families out of poverty.
"The SNP Scottish Government is doing what it can to tackle child poverty. The Scottish Child Payment has lifted 90,000 children in Scotland out of poverty and is expected to reduce child poverty further, and it is protecting Scottish families from Westminster's bedroom tax and housing benefit cap.
"But Westminster policies like the two-child cap continue to undermine the Scottish Government's efforts - and this will continue to be the case whilst we remain under Westminster control and without independence."