The gap between rich and poor is at its highest level for 20 years and is growing - with children hit hardest, a report said.
The global gap between rich and poor children has increased by 35% since 1990, the Born Equal report by Save the Children found.
More than twice the number of poor children die before the age of five than rich children in some countries, it said.
The aid agency calculated the household income per child in the top and bottom 10% of the income scales within 32 countries across the world.
These disparities are not limited to low-income countries, as low-income children from rich countries such as Canada are 2.5 times more likely to have problems with vision, hearing, speech or mobility.
The report comes as Prime Minister David Cameron co-chairs a UN panel on global poverty and development in London.
Mr Cameron, who is co-chairing the event with Liberian president Ellen Johnson Sirleaf, and president Susilo Bambang Yudhoyono, of Indonesia, will be discussing the global development agenda post-2015.
Despite a drop in extreme income poverty globally, which has dropped from two billion in 1990 to less than 1.3 billion today, Save the Children is calling for more to be done to narrow the gap.
Heidi Hautala, minister for international development in Finland, said: "In 2015 we, the international community, have an opportunity to rectify these inequalities. By placing inequality front and centre of the new international development framework we have the opportunity to stem the tide of rising inequalities and to give every child a better start in life."
Save the Children's chief executive Justin Forsyth, said: "In recent decades the world has made dramatic progress in cutting child deaths and improving opportunities for children; we are now reaching a tipping point where preventable child deaths could be eradicated in our lifetime. But this will only happen if we redouble our efforts and tackle inequality."