Children of Phnom Penh, David Barboza, The New York Times
Many children living in poverty are forced to work to support themselves and their families.
A large proportion of the world's 218 million child workers are in India, which came sixth in the poll.
"An estimated 60 to 115 million children are classified as working children - the highest number in the world," said Anuradha Mittal, director of the Oakland Institute think tank.
"Deprived of their childhoods, most have never seen the inside of a school."
U.N. Deputy High Commissioner for Refugees Wendy Chamberlin highlighted the case of Nepali girls who are trafficked to Indian cities, including Mumbai and Calcutta, for sex work. "They are really trapped," she said.
In Russia's breakaway Chechnya republic, fighting has displaced at least 95,000 people and UNICEF says 99 percent of residents live below the official Russian poverty line.
Child soldiers and forced labour were key reasons why respondents picked Myanmar, where the military junta is accused of conscripting tens of thousands of children to fight.
Egeland called on the international community to boost efforts to tackle children's issues around the world. "We must do more to achieve the Millennium Development Goals, particularly as they relate to children, who are, of course, our future," he said.