The report, titled Stop the War on Children, found 110 non-state actors were recruiting kids in 2020, up from 85 the year before.

That continues a concerning trend, with that figure having nearly tripled in a decade being up from 38 in 2010.

The study also found the recruitment of children in conflict zones is at an all-time high, with those at risk of recruitment having more than tripled in the last 30 years.

One in eight children live within 50km of an area where children have been used in conflict, equating to 337 million globally.

Save the Children chief executive Inger Ashing said the pandemic had put more children at risk.

"Violations against children in armed conflict do not stop during a pandemic. If anything, they get worse," she said.

"Worldwide, the countless children left without caregivers, out of school and in danger face a higher risk of violations."

Of countries worst affected, some 98 per cent of children in Afghanistan were at risk of recruitment, with Syria (97 per cent) and Yemen (89 per cent) close behind.

It was also found 22 governments were recruiting children, down from 25 the year before.

The UN called on governments to uphold conflict standards, hold perpetrators to account, take practical action to protect children and support their recovery.

"Children's rights are non-derogable in conflict and peace. They cannot be paused or cancelled," Ms Ashing said.

"Over recent decades, our knowledge about children's rights has increased ... the international community now needs to transform this raised awareness into collective action."

Australian Associated Press