UNICEF says one in three children worldwide cannot have their existence legally verified with a birth certificate since their birth was not registered.
Almost 230 million youngsters under the age of five have no birth certificate, which puts them at a disadvantage for procedural matters and leaves them more vulnerable to abuse.
"Birth registration is more than just a right. It's how societies first recognize and acknowledge a child's identity and existence," said deputy UNICEF executive director Geeta Rao Gupta.
"Birth registration is also key to guaranteeing that children are not forgotten, denied their rights or hidden from the progress of their nations," she said.
So "we recommend a registration system that is free, universal in coverage and confidential."
When natural disasters separate parents and children, reuniting families is much tougher when birth certificates are lacking, the UN agency stressed.