"I say I don't have a father," he explained.
It is impossible to say exactly how many women were raped during the genocide – the majority of them were subsequently killed and many survivors prefer not to talk about it.
It is equally difficult to estimate the number of children born of rape since 20 years after the genocide – in which an estimated 800 000 people, essentially Tutsis, died – the subject is still very much taboo.
"Rape was the rule and its absence the exception," said a United Nations Human Rights Commission report in 1996. "Unfortunately, there are no statistics … rape was systematic and was used as a weapon by the perpetrators of the massacres."
After his initial "surprise" and "anger", David said he "had no choice but to accept" that he was born from a rape and would like to know more.
"My mother is very light-skinned and I am darker. I'd like to know what he looks like," he said of his father.
"He doesn't know all the details and he has stopped asking questions," explained Ester, his mother. "My son doesn't talk a lot. It's difficult to know what he is really thinking."
Ester, a Tutsi, fled Kigali when the genocide carried out by majority Hutus began on April 7 1994. She was raped by a militia fighter in the border town of Cyangugu as she tried to cross into Democratic Republic of Congo with a group of other women.
"A woman proposed to hide us in a house but she tricked us and called the local militia chief," she recounted. "We spent a hellish night in that house."
When she realised she was pregnant the only person she dared confide in was her younger sister.
"After my son was born I told myself I had no choice but to love him," she explained. It was only after learning that her rapist infected her with HIV that she told her son the truth.
"Rape is still a taboo subject … but people are starting to talk about it. Things are changing even if there is still a long way to go," said Samuel Munderere of the NGO Survivor Fund (SURF), which helps rape victims and their families.
"A lot of children don't know about their past as their mothers refuse to talk about it," he said.
Nineteen-year-old Nyiramwiza "decided not to ask any more questions" about her father when she saw how distressed her mother became.
"The first time I asked about him eight years ago, my mother said nothing and started crying," she recalled, sitting in a small mud-brick house on the outskirts of Kigali, an impenetrable look in her eyes.
The following year when she repeated the question, her mother said that he had been killed during the genocide.
"I haven't told her the whole story because I don't want to upset her," said her mother, 42-year-old Augustine, almond-shaped eyes in an emaciated face.
Nyiramwiza was born shortly before the genocide started. Her father is a Hutu shopkeeper and former militiaman who kept her mother, a Tutsi, as a sex slave for a year in 1993.
Augustine was raped a second time during the genocide "by many men over a period of many days". She gave birth to a second child, a boy.
"After the genocide I hated everyone and I hated myself," said Augustine, who lost her whole family in the killings.
"I didn't love my children because they were a constant reminder of what I had been through," she said, wiping away silent tears.
She later discovered she had HIV. She knows her daughter is not HIV-positive but her son has refused to get tested. He had difficulties in school and "used to run away from time to time and be very aggressive," Augustine said.
Emilienne Kambibi, a trauma counsellor with SURF, which helps rape victims and their families, said Augustine's two children are "refusing to accept reality".
"The child is always ashamed to be the child of a militiaman and tends to reject his identity," Kambibi said.
Children born of rape during the genocide are reminded of their past every day, be it through seeing the mother's trauma or through rejection by the community in a country due to mark 20 years since the massacres this month.
It is difficult to know exactly how many children are affected because "a lot of them don't know about their past as their mothers refuse to talk about it," explained Samuel Munderere of SURF.
Not considered survivors
Keeping the past hidden has become harder since the time of the gacaca, the grass roots tribunals that between 2001 and 2012 tried some two million alleged perpetrators. In the process, the tribunals exposed some incidents kept secret by survivors.
"Such children are often rejected both by the mother's family and by the father's," explained Jean-Pierre Dusingizemungu, the head of the survivors' association Ibuka.
Children born of rape are not considered survivors because they were for the most part born after December 31 1994.
They are therefore not eligible for government assistance with their studies from the National Assistance Fund for the Needy Survivors of Genocide (FARG).
"FARG should help them. Their story is directly linked to the genocide. They are our children," Dusingizemungu added. – Sapa-AFP