In the sandy compound of his extended family's home, six-year-old Manuel Rafael is playing with his cousins. He almost makes it out of the compound's rickety gate but is pulled back to sit with the adults. He doesn't know he is HIV positive, and doesn't understand his grandmother's explanation in Portuguese about how he could have died but for the anti-retroviral (ARV) treatment he began when he was just a year old.

"He was very sick with vomiting and diarrhoea. Since he went on to ARVs I've seen a lot of change in the boy. Before he had no appetite, but now he can eat, sleep well and play with other children," says his grandmother, Raulina Mutheto, as she pulls the wriggling boy, dressed in his ragged shorts and vest, on to her lap.

Like an increasing number of children across sub-Saharan Africa, he is being cared for by his grandmother. His father died of Aids while his mother is also HIV positive, but she is on ARVs and has managed to keep her job as a housekeeper, leaving her mother to care for her son. Once a month she walks to the clinic with Manuel for his check-up.

Manuel is lucky. Latest estimates from the Mozambique government show 1.5 million Mozambicans with HIV, with only 15,000 on ARVs as the government attempts to build up a national programme of treatment. It is a race against time as the country struggles with a prevalence rate of 16% - lower than many of its neighbours such as Swaziland and South Africa - but still increasing at the rate of 500 new infections every day. Already between 2 million and 3 million people have died.

In most cases, ARV treatment for children leads to a dramatic improvement but paediatric programmes in Africa are in the early stages. The drugs come in adult dosages and the only option is to break the tablets in half, a crude measure where precision is important.

When the child is very small, the drugs have to be given in syrup form and as the child puts on weight, the dosages have to increase. In homes such as Manuel's with no running water, just keeping syringes clean and remembering the doses can be very difficult.

Health crisis

Fewer than 1% of the children who need ARV treatment are getting it in Mozambique, and most of them are in the capital, Maputo, and the surrounding shanty towns. The health system cannot cope: there are 700 doctors to serve a population of nearly 20 million and in many rural areas, one doctor - or a less qualified clinical officer - can be expected to cover 200,000 people.

On the other side of Maputo from Manuel, luxurious gated communities are sprouting along the beachfront. But beside them, in the sandy wasteland that the developers have not yet reached, the fragile huts of mud and bamboo teem with children. In the tiny compound of the Mulhanga family, there is no shade against the midday sun but for a ragged blanket strung across a corner where a cooking pot simmers.

Family secret

Celestina is 12 and HIV positive. She stands beside her mother, Luisa Mulhanga, while her siblings are sent away - they don't know that their mother, father and sister are HIV positive. "I was very sick last year and went to a health centre and did the test. Last year I began anti-retroviral treatment. My husband also. I don't remember when Celestina was tested - I have mental problems."

Luisa suffers from paranoid delusions - a symptom sometimes associated with HIV. Unlike many children infected with HIV/Aids, Celestina knows she has the infection. Throughout the interview, she is coughing. "She is taking treatment for tuberculosis and when that has been treated, she'll go on to ARVs. Before, she had a fever but she is getting better," explains her mother, "but when I'm sick I can't walk and the clinic is too far away for her father to carry Celestina - it takes an hour to get there."

As with many other children with HIV/Aids, Celestina's health is at further risk because her parents are also sick. Missing clinic appointments or forgetting pills is a big concern of those working with HIV in Africa; miss too many pills and HIV can become resistant to the drugs. This issue, known as adherence, is a particular problem for the growing number of HIV-positive orphans, says Dr Marc Biot, the medical coordinator of Médecins sans Frontières Luxembourg's HIV programme in Mozambique.

There are hundreds of thousands of orphans due to Aids in Mozambique alone (11 million across Africa) and that number is expected to soar in the next few years. Many are taken in by relatives, but in poor families they are likely to be the last in line for food or education. If they are HIV positive, as an increasing number are, they are very unlikely to get the treatment they need.

In many orphanages, the scale of the problem is beyond their resources. Steve Lazar, an Australian Christian minister who runs an orphanage outside Maputo for 430 children, admits: "In theory, we could test all the kids and put them all on ARVs but we don't have the staff for that. We guess that about 20% of the children are HIV positive. If a child gets sick and doesn't respond, then we will do the test. So far, 16 are on ARVs. There's a staggering improvement in the health of the children after going on treatment."

A year ago, Lija arrived at his orphanage after her mother had died. HIV positive and suffering from tuberculosis, she was so frail that Mr Lazar thought she could die at any time. But the improvement has been dramatic after going on ARVs. Now, she is like any inquisitive six-year-old, rummaging in the videos for her favourite while her playmate, five-year-old Ernesto, also on ARV treatment, settles down with his wax crayons to draw a horse. He's seen a horse once in the zoo and now he wants to ride one. These two, at least, have a future.