A UN study has found that children with disabilities are the most marginalised in the world.

The UNICEF report The State of the World's Children (2013) suggests that disabled children are more likely to suffer from a lack of education, and from poverty, hunger, and physical and sexual violence, because of their disability. In many countries, they also face abandonment or institutionalisation.

The best estimate for the number of disabled children globally suggests that some 93 million - one in 20 under the age of 14 - live with a moderate or severe disability, although this figure is likely to be a significant underestimate.

Globally, only ten per cent of children with disabilities are in school, and of these, only half finish their primary-school education.

"There is no group of children who are not just left behind, but nearly invisible, as much as children with disabilities," the executive director of UNICEF, Anthony Lake, said. "They're not registered at birth; they're bullied, they're discriminated against; they're sometimes . . . murdered."

Malnutrition is identified as frequently the hidden cause and effect of disability. About 165 million under-fives are believed to be chronically malnourished, leaving them short of vital vitamins and minerals. Anaemia, often linked to poor nutrition, is one of the most common causes of disability in the world. And, each year, up to half a million children are at risk of becoming blind because of vitamin-A deficiency, while a lack of iodine can lead to brain damage.

The report calls for changing attitudes, inclusion, and better social services for disabled children. More emphasis should be put on what the children were able to do rather than what they cannot do, Mr Lake said. "The greatest barrier they face is not so much the disability as the discrimination they face. So unless you tear down the barriers against their being included in society, and unless you provide assistance . . . they are not going to make it."

The report was launched in Da Nang, a city in central Vietnam that is strongly associated with Agent Orange. The airport was used to store the herbicide during the war with the US. Experts have linked a dioxin present in Agent Orange to an increased prevalence of disabilities in the area.

The UNICEF report urges governments to ratify and implement the Convention on the Rights of Persons with Disabilities and the Convention on the Rights of the Child: 27 countries, including Iraq, Somalia, and Zimbabwe, have yet to ratify the Convention.

UNICEF has launched a social-media campaign, #ThisAbility Portraits. It urges people to upload photos "of yourself, of a friend . . . or someone who inspires you" (statigr.am/contest/prwy/thisabilityportraits).