One in three of the world's children – 230 million under the age of five - do not have a birth certificate, effectively cutting them off from accessing life-saving health care services.
Uncounted and Unreached finds that governments have enormous data gaps and are using inaccurate statistics to plan funding for midwives and where and when new health facilities are built.
World Vision's Senior Health Advisor, Dr Tari Turner, said that birth registrations are not common in many developing countries and this impacts whether or not children see a doctor during their first five crucial years of life.
"Children are being born and dying, invisible to those who make decisions affecting their health, wellbeing and futures. They slip through the cracks because there are not enough doctors, not enough trained midwives, not enough medicine and because governments underestimate or misunderstand their needs," Dr Turner said.
Amongst the most at risk are indigenous children and ethnic minorities, child labourers and trafficked children, orphaned and homeless children, children with disabilities and refugee, stateless and internally displaced children.
The report recommends that community-driven statistics and monitoring services should lead the way in helping governments to improve counting. It cites that in Indonesia, a community initiative helped to map how many young children lived in the local area and subsequently, the location of the local growth monitoring centre.
World Vision Australia's Chief Executive, Tim Costello, said that children have the right to be counted and to receive basic healthcare no matter where in the world they are born.
"It is a basic right for a child's life to count and for that child to be able to reach essential healthcare services. Invisibility immediately puts children at a disadvantage during their early development which is the most critical stage of a child's life," Mr Costello said.
Some 6.6 million children under the age of five die each year from preventable causes. As part of a final push towards the Millennium Development Goals, set to expire at the end of 2015, World Vision's report calls on governments to urgently improve civil registration and vital statistics systems, and to put families and communities at the centre of efforts to count and reach vulnerable children.