By Jane Dreaper
BBC Health Correspondent
There are 1,200 children in the UK with HIV
Some 24,000 people are gathering in Toronto, as the International Aids Conference gets under way.
Sunday's opening concert featured Alicia Keys and the Barenaked Ladies.
The burst of upbeat music sums up one of the key themes - how HIV affects young people.
This problem doesn't just belong to developing countries - there are 1,200 HIV-positive children in the UK.
A London charity which supports young people with the virus is beginning an awareness and fundraising campaign.
I visited the Body and Soul project, and met Crystal, an attractive and chatty 19-year-old.
She was told six years ago that she'd been born HIV-positive.
"I used to come to this project with my mum, so I just thought it was a youth club.
"When they told me I was HIV-positive, it was a shock. I felt sick when they told me, to be precise.
"Then things started coming into my head - like - oh that's why I've been taking medication all these years.
"At that time I didn't know what HIV was. I just really thought about death - I thought you get HIV, you get Aids and then you die."
And Aids has cast a shadow over the life of this confident young woman - Crystal's parents, who were Ugandan, have both died from the disease.
She does not tell college friends that she is HIV-positive, though she tries to spread the word about safe sex.
"I've got a lot of friends who don't use condoms - and I've known a lot of people that have caught infections," she told me.
"I try to educate my friends to tell them it is important to use a condom because these days you don't really know anything - it's better to be safe than sorry."
Crystal is continuing her studies and loves dancing. She is aware that some difficult decisions lie ahead.
"I would like to have my own family - but I'm dreading it because it could be complicated for me to have kids. But I would like to have a big family."
Crystal's nervousness is understandable - though doctors say that if HIV-positive women take anti-retroviral drugs during their pregnancy and avoid breast-feeding, the chance of their baby carrying the virus is tiny.
I also met Natasha, who is 17 and first found out she had HIV when she was 12. She felt really scared and frightened.
It seems most children with HIV do not learn about their condition until their teens - doctors and other experts generally support this idea, because of the stigma that still surrounds the condition.
And parents often fear that their children will blurt out their secret in the playground - and then get shunned.
Like Crystal, Natasha hides her medication from friends at college.
"It's hard - they are always asking: 'Why are you taking your tablets? I make up all these excuses," said Natasha.
Crystal and Natasha have greatly benefited from the advances in HIV medication, and they should be able to live long lives.
But Rosie Turner, who helps run the Body and Soul project, is outraged that ignorance about HIV means these young women shroud their condition in secrecy.
"There is so much hatred towards it - it is very very different to something like cancer where people are surrounded by love, care and support," she told me.
"Within HIV, our families are living in a separate world, and having to lie."
Discretion is hugely important for Body and Soul - the charity operates from an unmarked building.
It has begun a campaign to say it is OK to smile at someone with HIV.
Rosie added: "The Smile campaign is trying to put a more positive slant on HIV and Aids. We're subtly trying to break down hostility, by saying it's OK to smile, as well as to care for that person."
Kathy Burke, James Nesbitt and Thierry Henry are among the famous names taking part in the campaign.
And it looks as though the charity will try to tie up with special new services being launched by doctors - but covering much more than health needs.
At St Mary's Hospital in London, health professionals treat about 200 children with HIV at a family clinic.
But they have realised that the brightly painted walls and children's toys do not provide the best setting for helping the first generation born with the virus who are now reaching adulthood.
Just a few years ago, these youngsters had not been expected to survive.
Dr Simon Portsmouth is starting a clinic for about 75 teenage patients - he admits it's uncharted territory.
"They're a very different group of patients to our usual ones, " he explained.
"They have probably only just learned of their diagnosis - perhaps at the age of 12 or 13.
"They are going to school with their peers who may be becoming sexually active at that age - they have all of those concerns.
"And because the virus can affect the brain, about a third of these young people may have learning difficulties - and so their social needs are going to be quite great in the future."