In the shade of the village mango tree, near Morrumbala in central Mozambique, more than 20 children, some as young as eight, have dissolved into giggles.
In the mid-day heat, Ameila Zeca, their teacher, is struggling to roll a condom over a chewed corn husk. When the rubber rips, she turns her attention to the arm of a chair. By then, the village headman monitoring this culturally-sensitive sex education experiment, and a host of parents watching shyly from the shade of another tree, are also smiling.
"Does everyone know about Sida [Aids in Portuguese]?" Ms Zeca asks. The laughter subsides. She drills them in ways the HIV virus can be contacted. "Does anyone want to die?" she asks. "No" the children chorus, no one wants to die.
This village, like every other in Zambezia province, is struggling to stitch itself back together following the country's 17-year civil war. Just a few years ago, the area was deserted. Millions fled across the border to Malawi to escape the fighting between Mozambique's Frelimo government and South African-backed Renamo rebels. Houses were razed and villages massacred. Millions died until neither side had the energy to slug it out any more.
After peace was brokered in 1992, the refugees streamed back from Malawi. The past echoes on in the mortared buildings and the fenced-off mine fields along the verges of the few pitted, surface-stripped roads. The war bankrupted Mozambique, but its economy is showing signs of recovery and in Zambezia's rural mud settlements and small towns, communities seem to be kick-starting.
But all these precious signs of progress are threatened by a new enemy; Aids. The disease in Mozambique is most advanced in Zambezia. The refugees carried it back there from Malawi, which boasts one of the worst rates of HIV infection in sub-Sahara Africa.
New United Nations statistics, released to coincide with World Aids Day today, show that of the 30.6 million people in the world who are now thought to be HIV-positive, a shocking two-thirds are in Africa.
In the West, education, good health care and the discovery of expensive, life-prolonging combination therapies have robbed the virus of some of its sting.
In Africa by contrast, Aids is claiming victims at breathtaking speed, ploughing through countries whose populations are too worn out to offer much resistance to the disease. Charities such as Save the Children, sponsors of the village sex education scheme, are battling against enormous odds.
Apart from poverty, the disease in Mozambique can count on factors such as the low status of women and children to aid its advance. As we crawl in our car along crumbling roads, Etelvina da Cuhna, Save The Children's local project director, points out child mothers as young as 12 tilling the soil in the nearby fields with their babies on their backs.
"In towns, men usually have two or three wives and in rural areas as many as six," she says. "Girls marry as young as 10 often to much older men. Three out of 10 girls are married before they reach the age of 12."
Ms da Cuhna dispenses condoms in the villages as we tour the district. The men look unimpressed. Some believe "Sida" is a government conspiracy to curb their traditional polygamy. Those who do accept the condoms do not always use them for their proper purpose. In some villages we see boys kicking footballs made of blown-up condoms, rope and banana leaves.
The men have girlfriends and prostitution is widespread. Ironically, the post-war recovery is helping to spread HIV infection. Morrumbala is again teeming with people and the local brothel does a roaring trade. Every week a lorry arrives in town to pick up "used" women and deposit another consignment of girls.
The presence of international charities drew one local girl called Anna, 25, to Morrumbala. She found work with the UN High Commissioner for Refugees. But it wound up a couple of years ago, and the Italian aid worker she was living with returned to his wife. Now she now trawls the bars. If not, she does not eat. It is the fate of so many local women. "There is no other work," she says. Competition for clients is fierce, but she still sympathises with her rivals. Girls as young as 10 work the bars just to go to school. "They swap sex for money for exercise books" she says. "I really feel for them." Like her they seldom use condoms because most of their clients refuse.
The pieces are all in place for a terrible epidemic. Sexually transmitted diseases are widespread and largely untreated (increasing vulnerability to HIV). There are no reliable statistics but local Aids workers reckon the HIV infection rate among pregnant women is around 25 per cent.
That the local health services are ill-equipped for the crisis is an understatement. Malaria and other diseases which long ago ceased to trouble the West have them beaten. Morrumbala has just witnessed an outbreak of bubonic plague. "There are no needles, no aspirin, no antibiotics," says one official, who does not want to be named, "except when an official visits."
In the face of such a bleak reality, Save The Children believes the only hope is target the next generation as early as possible. Their controversial sex education pilot only started after they had convinced parents that their children not only knew about sex but were sexually active.
Even with education, the children who chant about Sida beneath the tree face heavy odds. The social standing of women is unlikely to improve unless the economy takes off. Until then, girls and women will not have the luxury of choice or the power to insist on a condom.