Only one HIV-positive child in 20 in developing countries receives the treatment they need, a report by children's campaigners has found.
Most children contract HIV from their mothers
Coming together as the Global Movement for Children, they said the international community must urgently address the problem.
Group chairman Dean Hirsch, said the lack of treatment amounted to a death sentence for millions of children.
He warned most of HIV-positive children die before their fifth birthday.
The report has been compiled by Oxfam, Plan International, Save the Children, Unicef, World Vision ENDA Tiers Monde, the Latin America and the Caribbean Network for Children.
It says too few drugs are available in formulations that are affordable and able to be administered to children, while the development of new drugs continues to focus mainly on adults.
More than 90% of children with HIV live in sub-Saharan Africa - they have the least access to treatment, the report said.
It continues the "profit-driven climate of drug development" means there is little incentive to develop child-specific formulations of anti-retroviral drugs for children, and that therefore child-appropriate treatment is "practically non-existent".
The Global Movement for Children said that, in June 2005, around four million children were in need of cotrimoxazole, an antibiotic costing 3 US cents per day per child, which prevents life-threatening infections in HIV infected children and infants born to HIV-positive mothers.
It can also delay the onset of Aids and the need for anti-retroviral therapy.
It adds that 90% of HIV-positive children are infected by a failure to prevent mother-to-child transmission.
The report says providing a mother with comprehensive care can reduce the risk of transmission to less than 2%.
But under 10% of HIV-positive pregnant women currently receive the necessary drugs.
The report makes a series of recommendations including the development of simple and affordable diagnostic tests, more research and development for child specific treatment and improvements to health-care systems in developing countries to make it easier to get medication to children.
Children's worlds 'shattered'
Mr Hirsch said: "These children are missing out on treatment because they are missing from the global Aids agenda."
Ann Veneman, executive director of Unicef, said: "Children are the missing face of HIV and Aids.
"Millions have watched their worlds shatter around them because of this disease, losing parents, teachers, a sense of security and hope for the future.
"Children affected by HIV and Aids are often discriminated against and face enormous odds.
"Through strengthened partnerships among governments, donors, international agencies and the private sector, we must do everything possible to ensure that drugs, diagnostic equipment and resources are available to treat children."
Thomas Miller, chief executive officer of Plan International said, "Unless the world takes urgent account of the specific impact Aids has on children we will fail to meet the Millennium Development Goal - to halt and begin to reverse the spread of the disease by 2015."