Only one child in 20 with HIV has access to treatment, according to a report from children's charities.
By Robert Few
Here, one girl describes her life with HIV.
Noo is 12 years old. Her father is dead, as is her mother.
Campaigners say too few children receive the drugs they need
They both died of Aids-related illnesses, and the HIV virus was passed on to Noo - whose name has been changed to protect her identity.
Orphaned, impoverished and HIV-positive, she lives with her grandfather, who is an alcoholic.
In some ways, Noo looks much younger than her age, because the virus has left her painfully thin and has sapped her strength.
But in her eyes and in her casual use of medical terms like "anti-retroviral" and "opportunistic infection", she seems much older.
'Grandfather was drunk'
Noo runs the household.
She does all the cleaning. She manages the finances, hiding money from her grandfather and giving him an allowance for necessities.
Noo has to travel 70 kilometres to collect her medicine from her village in north Thailand.
She says: "I have been ill for about a year. I feel breathless and I cough.
"I went to the local hospital and the doctor said I had an opportunistic infection. I went with my mother because she was still living then.
"They did some tests, but I didn't know what was going on. The doctor didn't know either, so I went to Chiang Mai Hospital.
"There they told my mother I had HIV.
"I knew that HIV meant Aids and it made you weak.
"My mother died that year.
"After that my grandfather was drunk all the time and he used to hit me and shout at me a lot.
"For a while I stayed in a foundation, but my grandfather missed me.
"Now he just drinks a little but he can still work.
"He takes me to eat every day and sends me to the bus to come to a community group called Aids Access."
"Now I am taking anti-retroviral drugs every day.
"I have to take them at 7am and 7pm. The doctor told me to take them at the right time.
"I have been taking them for four months and now I feel stronger - and I can eat.
"I go to see the doctor once a month. I go on my own and that's OK, but when I come back I have to carry all the medicine myself.
"The healthcare worker gave me a watch to help me take the drugs at the right time.
"The watch is very useful because it rings every time I need to take my drugs. Otherwise, I would forget.
"If I forget to take them, I have to take them as soon as I remember."
'I want to be a business-woman'
She adds: "I am not afraid of Aids. If I take my drugs the disease gets better.
"It will never go away, but if I take my drugs, I won't be sick."
"When my friends knew I was sick, they would not come to play with me because I was so thin and they said, 'Don't come and study with us because you have Aids'.
"But I know that Aids is not something you can get easily, and you can't get it from playing.
"Now they understand, and they come to see me at home or I go to see them. Their parents let us play together.
"I don't really go to school because I don't feel well. The teacher wants me to get a bit better before I go back to study.
"I am waiting for next year.
"I want to study and I want to be a business-woman.
"I am 99% sure that I will be strong enough, but I can't be certain because I have a lung problem, and in the cold and rainy season I can't breathe very well."