Nicholas Karikarisei, a fisherman, cares for his six children in a two-room home in Nigeria's Niger Delta.
Last year, he took his 4-year-old son, also Nicholas, to the state hospital to be treated for malaria, a disease that can be fatal.
The state hospital is free for children under five, he says, but his family, like many others, was turned away because he couldn’t prove Nicholas’s age. He had no birth certificate so he had to pay a private hospital $45 for treatment in a region where most people live on less than $1 a day.
"The awareness was not there. The importance was not there," he says. "It’s only when I came to get my son medical attention in the government hospital, only when I showed up there [I learned], 'no birth certificate, no free medical services.'”
According to UNICEF, one in three children worldwide does not "officially exist,” and nearly all of them live in Asia or sub-Saharan Africa.
The U.N. children's agency also says 60 percent of Nigeria's children — about 17 million — lack birth certificates, a figure second only to India, which has 71 million unregistered children.
UNICEF child protection officer Sharon Oladiji says the problem is particularly acute in rural northern areas, where Nigeria's undocumented children are often denied healthcare, education and are especially vulnerable to rights abuses.
“It’s a patriarchal society and most women do not take part in decision making at all, and most women in the very rural north aren't educated, so they don’t know the importance of registering their children,” she says.
Aside from facing a host of difficulties such as denial of government services, children least likely to be registered are the ones most likely to face adverse life circumstances.
Health workers must know a child’s age in order to provide treatment safely, for example, and trafficked children, many of whom are undocumented, cannot prove their age when interacting with legal authorities.
“When a child is in contact or in conflict with the law, you don’t treat that child like an adult that has committed a criminal offense," says Oladiji. "There’s a separate legal framework to deal with children who are in conflict with the law.”
Nigeria's lack of birth records also undermines government efforts to track vital demographic information, making it especially difficult to prevent children from dying if officials cannot accurately determine how many have died in given region, or what the cause of death might be.
UNICEF is currently trying to convince traditional leaders and families of the importance of registering children. In northern Nigeria, where most of the families are Muslim, Oladiji and her colleagues sometimes present verses from the Quran that suggest registration is encouraged by Islam.
their argument that, for example, birth registration facilitates a child’s future ability to make the Islamic pilgrimage to Mecca.
“We want to look at what they do, what they like," she says, explaining that they also associate registration with Muslim pilgrimage.
"For example, going to Mecca, we link with that: 'This child, if you don’t register his birth, he cannot get a passport. He cannot go on a pilgrimage.’”
But for many parents, the importance of registration simply hadn't been made clear. Karikarisei, the father of six, said he has no objection to registering his son, but that the nearest registration center was 15 hours from his village.
UNICEF says it hopes to dramatically increase the number of registration centers in Nigeria, and that 65 to 70 percent of Nigerian childrens will receive birth certificates within the next few years.
Hilary Uguru contributed to this report from the Niger Delta