Coronavirus and its related lockdown measures have pushed 150 million more children into poverty, according to analysis published by UNICEF and Save the Children.
Since the start of the pandemic, there has been a 15 per cent jump in the number of children living in deprivation in low- and middle-income nations, taking total numbers to around 1.2 billion, the organisations say.
The report notes the world's poorest children are getting poorer and warns the situation will likely deteriorate further in the coming months.
"Families on the cusp of escaping poverty have been pulled back in, while others are experiencing levels of deprivation they have never seen before," UNICEF executive director Henrietta Fore said on Wednesday.
"Most concerningly, we are closer to the beginning of this crisis than its end."
The agencies called on governments to rapidly expand social protection systems, access to health care and remote learning opportunities.
"Children who lose out on education are more likely to be forced into child labour or early marriage and be trapped in a cycle of poverty for years to come," Save the Children chief executive Inger Ashing said.
The analysis looked at data from more than 70 countries on whether children are deprived of education, medicine, housing, food, sanitation and water.