A new report by Save the Children and UNICEF has found that four million more children a year are living beyond their fifth birthday than in 1990.
Research by the Overseas Development Institute shows that aid is a key factor in improving children's well-being around the world.
It says economic growth and good government policies also help improve their life-chances.
Children in Brazil, Bangladesh and Vietnam have made great improvements.
The report identified six key influences on the improvements seen over the past two decades.
But Save the Children says it is hard to show the exact impact of aid on its own, because it generally works best when used alongside good governance and economic growth.