The United Nations' children's agency has warned that 69 million under-fives will die from preventable causes between now and 2030 unless countries speed up action to improve health and education for the most disadvantaged.
Unicef's annual State of the World's Children Report, said that based on recent trends and projected population growth, 167 million children would also live in extreme poverty, 60 million would not be attending primary school and 750 million women would have been married as children by 2030.
The agency's deputy executive director Justin Forsyth said Unicef was "broadcasting our message into a world that is more hostile", especially to migrants and refugees, including millions of children.
Many are fleeing because of poverty and inequality, he said, and these root causes must be addressed "if you're going to stop some of these forces overwhelming particular countries and polarising the political debate".
"Our job in Unicef is to be there on the ground and helping children survive," Mr Forsyth said, but the agency also needed to ensure that there was "a factually-fuelled debate about these tough issues of our times" and the message got out that focusing on the most disadvantaged was crucial.
Unicef programme director Ted Chaiban said that in addition to youngsters fleeing poverty and inequality, there were also more children living in conflict areas - 250 million - and 30 million were displaced.
Inequality existed in every country, he said, and globally children in the poorest 20% of the population were twice as likely to die before the age of five than those in the richest 20%.
"Eighty per cent of preventable deaths now occur in south Asia and sub-Saharan Africa, with almost half occurring in India, Nigeria, Pakistan, Congo and Ethiopia," Mr Chaiban said.
Unicef called on all 193 UN member states to develop national plans that put the most disadvantaged and left behind children first and set specific goals to close gaps between the richest and poorest.
Mr Forsyth said up to 147 million children between one and five could be saved from preventable death "just with a 2% increase in expenditure in 74 countries".
Unicef also had evidence that every dollar spent on vaccinations for the most disadvantaged children "can generate 16 dollars in terms of economic returns", he said.
According to the report, cash transfers have helped children stay in school longer and on average, each additional year of education a child receives increases his or her adult earnings by about 10%.