They are called the "invisible children."
UNICEF says hundreds of millions of them are out of sight, out of mind, and out of reach. In its annual report on the state of the world's children, the organization says millions of them are suffering from severe exploitation and discrimination. And, as a result, they are living a nightmare, suffering not only from neglect, but from abuse.
There are millions living in miserable conditions because they don't have the protective safety net or they're not living in the right environment. These children are excluded from school, health care, and their right to a childhood, according to the report.
What's more alarming is that they have become invisible to the world, wiped off its radar.
Poverty, HIV/AIDS and conflicts were the culprits in last year's report. This year, it's a different story. It is now a culmination of these culprits and factors such as weak governance and discrimination.
The report says children "disappear" and are forgotten when they're in these four circumstances:
Children without a formal identity. UNICEF says more than 50 million children are not registered at birth. As a result, they have no access to education and health care.
Children without parental care. One in 13 children in the developing world has lost at least one parent. They grow up without the love and protection of their family or a family environment. Often these children live on the streets and are exposed to all forms of abuse.
Children in adult roles. The report estimates that 171 million children who are forced to work in hazardous environments, such as factories, mines and agriculture, miss out on a childhood.
Children who are exploited. About 8.4 million children work in the worst forms of child labor, including the sex trade. These children, the report argues, are the most "invisible" and impossible to track.
Ann M. Veneman, executive director of UNICEF, said governments must strive to meet the U.N.'s millennium development goals on reaching vulnerable children.
"There cannot be lasting progress if we continue to overlook the children most in need -- the poorest and most vulnerable, the exploited and the abused," she said.
At the current rate, 8.7 million children under the age of 5 will die in 2015, but if the millennium goal to reduce child mortality is met, 3.8 million will be spared.
So how does UNICEF aim to reach the developing world's vulnerable children? It all begins with the governments.
The report calls on countries to do more and says they need to reach out to these children in four key steps:
Research, monitoring and reporting: Abusers must be prosecuted and a child's well-being must be recorded, reported on and monitored.
Legislation: National laws need to be changed and matched to international ones.
Financing and capacity-building: More money needs to be allocated to institutions that serve children.
Programs: Schools must be open to all. Reform is required in many countries and communities to remove entry barriers, such as the requirement of a birth certificate to attend school.
The world must ensure that the most vulnerable child is not left behind because even the poorest children deserve a healthy and safe life.