File - Sudanese refugees cross into Chad near Koufroun, Echbara, on May 1, 2023. AFP
The KidsRights index, based on figures supplied by UN agencies, said children are also at risk from climate change and ongoing health impacts from the Covid pandemic.
"All the above amounts to a 'polycrisis' of extreme seriousness as children's rights and livelihoods continue to be torn apart by global pressures," said the Netherlands-based KidsRights.
The annual KidsRights Index is the only ranking that measures how children's rights are respected annually, ranking Sweden, Finland and Iceland as best out of 193 countries.
Chad, South Sudan and Afghanistan were the worst for children's rights, the Dutch NGO said.
Russia's invasion of Ukraine added to a series of pre-existing crises that are affecting the rights of children, the group said.
"One in four children across the world are expected to be living below the poverty line this year following the war in Ukraine, which has sent energy and food costs soaring across the world," the KidsRights report said.
Ukraine's 7.5 million children were the "most disproportionately affected by the war" including large numbers who were displaced, the report said.
Post-pandemic inflation and a global healthcare "crunch" after Covid had also had a negative effect, particularly on immunisations, it added.
A total of 67 million children had missed routine vaccinations between 2019 and 2021 due to disruption caused by the pandemic, it said.
Climate change remained a huge worry, with children in countries in Asia in particular facing "particularly high exposure to climate hazards, shocks and stresses".
The report also cited the civil conflict in Sudan and the banning of girls from higher education in Afghanistan.
Rising poverty was most likely the cause of increasing rates in mortality of children under 5 in countries such as Madagascar and Niger, and increases in child labour.
"This year's report is most alarming. Our promising next generation is being disadvantaged at every turn", said Marc Dullaert, founder and chairman of KidsRights.
He urged nations and aid agencies to take "immediate actions" to "protect children from this current catastrophe and to pave the way for a more positive and hopeful future."
The survey uses UN data to measure how countries measure up to commitments in the UN Convention on the Rights of the Child.