Sihle, from Johannesburg, lost her mother to HIVAids when she was 13. Her sister is HIV-positive.

“I had to take care of my sister and her baby. Sometimes I would leave school for a whole week to take care of them. The baby was only six months old so I had to wash the nappies, clean the house, everything... I got my report card last December, and it said ‘fail’. I was angry. I asked myself why do I have to fail?”

Martin from Uganda was motherless at 12, and orphaned by 16:

“When mother was sick, it was us who were looking after her... I left school for one term and then went back. Then my sister left school for one term and we traded back and forth like that. But even when I was in school.... my mind was back with my mother and it was not easy to concentrate.”

These are just two testimonies from children orphaned by Aids in a poignant and hard-hitting report by Human Rights Watch.

It was published just as Unicef, the United Nations children’s fund, this week launches its global campaign on HIVAids, the first to focus on the children left behind. Stephen Lewis, UN special envoy for HIVAids in Africa, said: “No one predicted the effect HIVAids would have on children.

Yet this is the greatest unanticipated single challenge of the pandemic.”

Unicef says there are around 14 million Aids orphans under 18 in sub-Saharan Africa. This could rise to 20 million by 2010.

In hard-hit countries such as Botswana and Zimbabwe, three-quarters of orphans lost their parents to Aids. But with the emphasis on treating adults, the needs of Aids-affected children, particularly their education, have been neglected.

“The question of getting the child into school and keeping them there is hugely important,” said Mr Lewis. “The tiniest cost stands in the way of education and is particularly disadvantageous to orphans because they have no source of income at all.”

The elimination of all school fees is part of Unicef’s campaign, which aims to meet the basic needs of 80 per cent of the world’s Aids-affected orphans,.

Human Rights Watch said governments had “turned their backs” on the education of Aids-affected children who are “less likely than their peers to enrol, attend, or advance in school” - even in Kenya and Uganda, which have free primary education.

Aids orphans in Kenya, for instance, attend informal schools, often with a “single teacher, virtually no scholastic materials and a complete lack of government support”, Human Rights Watch said.

Meanwhile there is a “frantic effort” to train teachers to replace those dying of Aids. “Teachers are heavily infected, and are infecting pupils,”

Mr Lewis said.

Unicef’s campaign will focus on preventing mother-child transmission of HIV, protection of children made vulnerable or orphaned, and preventing adolescents and young adults from becoming infected. Slightly more than half of new infections each year - 2.5 million cases - occur in the 15-24 age group. Three-quarters of these are girls and young women.

Yet this is an age at which prevention messages can really work, Mr Lewis said. The age group already has its own peer Aids-prevention exercises, often organised by young people themselves using music, dance, drama, poetry and drumming.

“Issues of late marriage, abstinence, condom use and so on are very real when everyone around you is dying,” Mr Lewis said.

The campaign is backed by the World Bank, the World Health Organisation, the Global Fund and the Clinton Fund, which is providing medicines.

Letting them Fail: Government Neglect and the Right to Education for Children Affected by AIDS, Human Rights Watch, October 2005