Now the 12-year-old is one of the most prominent AIDS activists in Latin America and a rarity in a region where few children are willing to break the silence and tell their classmates they have HIV for fear of rejection. She edits a children's magazine on the virus.
"The boys and girls who live with HIV are here and we are growing up with many goals," Keren said Sunday at the opening of an international AIDS conference where she shared the stage with Mexican President Felipe Calderon and U.N. Secretary-General Ban Ki-moon.
"We want to be artists, teachers, doctors - even get married and have kids. ... But achieving these goals will only be possible when we receive the attention we need, when we are guaranteed the medicines that we need, when we are accepted in schools."
Taking several deep breaths to overcome stage jitters, Keren delivered what was clearly the star speech of the conference's inauguration: Audience members repeatedly interrupted her brief, but moving words with loud applause and whistles, and followed her discourse with a standing ovation that lasted well after she left the stage.
In an interview with The Associated Press days before the conference, Keren talked matter-of-factly about the virus she has had since birth, flashing a dimpled smile and exposing a row of braces.
"It's like a little ball that has little dots, and is inside me, sort of swimming inside me," she said, curling her fist as she recalled what her parents explained to her with drawings long ago.
Keren's openness about her HIV status comes as the virus's victims grow increasingly younger.
Worldwide, people ages 15-24 accounted for 45 percent of people infected with HIV in 2007, according to the 2008 U.N. AIDS report.
In Latin America, 55,000 of the nearly 2 million people with the virus were under 15 years old, the vast majority of them infected by their mothers. Only 36 percent of pregnant women in the region receive medicine to prevent transmission, although that is an increase of 26 percent since 2004.
And while more than 60 percent of the adults with HIV receive antiretroviral drugs in Latin America, only about one-third of children do. Experts say less research and funding has been dedicated to medicine for HIV-positive children, who require smaller doses and additional medication to offset the aggressiveness of antiretrovirals.
Even so, children born with HIV are increasingly looking forward to long lives.
"There's a whole new generation of young people that were born with HIV that are reaching adulthood. It presents very interesting challenges," said Nils Katsberg, UNICEF'S director of Latin America and the Caribbean.
It won't be easy encouraging HIV-positive children to speak out in Latin America, where talking openly about sexuality is often taboo.
When she first started school, Keren's classmates refused to play with her. Speaking out about HIV made all the difference. At 9, she began accompanying her parents - founders of the AIDS advocacy group "Llaves" - on talks to schools. She has visited half-a-dozen countries to share her story.
Too often, children with HIV "live in a culture of secrecy," said Maria Villanueva Medina, a psychologist with Casa de la Sal, a group that runs an orphanage for children with HIV in Mexico City.
"They can't talk about their diagnosis in the school because they can be kicked out. They can't talk about it in their communities with their neighbors."
At Casa de la Sal, children are told about the virus around the same age as Keren was, but few dare to tell their schoolmates even where they live.
Casa de la Sal is adapting to a new reality. When it first opened 22 years ago, many of the children died by the time they reached their teens. Today, the orphanage has not had a death in eight years. The government provides antiretrovirals.
Faced with the challenge of preparing the children for adulthood, the orphanage eventually began sending them to regular schools instead of giving classes within the institution.
The hope is that someday, many will be outspoken advocates for their own cause.
"We need to start getting young people involved in leadership again in HIV and AIDS because it's easy to get kind of complacent," said Joe Cristina, whose Los Angeles-based Children Affected by AIDS Foundation helps fund the orphanage.
Keren writes an upbeat editorial each week. ("I want to congratulate all the boys and girls who have graduated and got good grades. Keep it up!!") She is now popular among her classmates.
She takes singing and acting lessons, dreams of going to Hollywood and breathlessly notes that she shares the same Zodiac sign - Sagittarius - and favorite color - purple - with her teen idol, Miley Cyrus.
"Sometimes I have so much fun that I forget I have this" virus, she said.
For more information visit the Web site of the XVII International AIDS Conference: www.aids2008.org.