Paula Donovan, co-director of AIDS-Free World, told CNN the report detailed testimonies from six children interviewed last year by staff from the U.N. children's agency UNICEF and the Office of the High Commissioner for Human Rights.
The children gave harrowing accounts of their own experiences and abuses they had witnessed, and they recounted the experiences of friends of theirs, she said. "There are a few cases where a boy describes the sodomizing of a friend by soldiers who are threatening to beat him if he tells anyone about what they are doing," Donovan said.
The abuses were allegedly committed against a dozen children at a displaced persons' camp at M'Poko International Airport in Bangui, the capital of the Central African Republic, between December 2013 and June 2014.
The shocking allegations have prompted French President Francois Hollande
to promise strong action if they are confirmed.
"If some soldiers behaved badly, I will be merciless," he said in comments broadcast by CNN's French affiliate BFMTV.
"If this information is confirmed, there will be exemplary sanctions."
Donovan said one boy recounted how a soldier who he'd asked for food had asked him to perform oral sex in exchange. When the boy refused, the soldier asked him to find a woman who would, she said.
Another boy told how a soldier took him inside an army base, overriding the objections of a guard, and sexually abused him there.
Donovan said the soldiers gave them small amounts of food, water and sometimes some cash in return for sex, adding, "The children were severely traumatized by the events."
The report was sent to her in recent days at AIDS-Free World, Donovan said, but she was not at liberty to say by whom. The advocacy group shared it with the UK's Guardian newspaper, which reported on the allegations late Wednesday, saying the report had "confidential" stamped on every page.
The document already had been leaked to French authorities last year.
A U.N. staffer has been suspended over the leak, a statement from the spokesman for U.N. Secretary-General Ban Ki-moon said Wednesday.
The unnamed staffer is accused of providing an unedited version of the internal U.N. report to French authorities before it even reached senior management in the U.N. Office of the High Commissioner for Human Rights.
According to the statement from Ban's spokesman, the alleged offenses occurred before a United Nations peacekeeping operation
in the Central African Republic, known as MINUSCA, was set up.
The interviews for the U.N. human rights investigation were conducted between May 5 and June 24 of last year, Donovan said.
The French troops were there under the authority of the French government, she said. But U.N staff still should act to protect children if they uncover evidence of sexual abuse and exploitation, she insisted.
"Certainly, the children should expect that the United Nations will not only protect them, but also provide the services which are so desperately needed by children who have been forced to have oral sex by a man with a gun in return for food," she said.
A French Defense Ministry spokesman told a news conference in Paris on Thursday that the army had not gone public about the case previously because a judicial inquiry was ongoing.
"Obviously, if these facts were proven, as you know, they are totally against our values, the values held by the French army," said Col. Gilles Jaron, adviser to the Army's Joint Chief of Staff. "Of course if these facts were proven, firm sanctions would be implemented against those responsible."
Pierre Bayle, a spokesman for French Defense Minister Jean-Yves Le Drian, said the minister had "decided there would be zero tolerance on all that is sexual violence."
Bayle added, "We're not trying to hide the facts, we are verifying the reality of the facts. We cannot say anything for now."
The spokesmen declined to comment on whether investigators had identified any suspects in the case or how many there might be.
Donovan said the children interviewed for the U.N. report had provided a lot of detail on their alleged attackers that could help an investigation.
"Several of the children gave very clear (descriptions of) physical characteristics or habits -- whether or not the soldier was a chain smoker, whether or not he had a tattoo, if he was tall or short -- very particular details that would allow any decent investigator to narrow the pool of suspects immediately," she said.
The French Defense Ministry said in a statement Wednesday that it had received the testimonies of Central African Republic children accusing French soldiers of exploitation and abuse in late July 2014.
"Given the detailed nature of the evidence and the extreme seriousness of the allegations, the Minister of Defence has responded by taking all necessary measures to ensure that the facts and possible criminal and disciplinary responsibilities can be established quickly," a statement from the ministry said.
An investigation was ordered, and the Paris prosecutor's office also opened an inquiry, which is ongoing, the statement said.
"The Minister of Defense has taken and will take all necessary measures to enable the establishment of the truth. If the facts should be proven, it will ensure that the strongest possible sanctions are imposed against the individuals responsible for what would be an intolerable offense to the values of the soldier."
The U.N. statement said the suspended U.N. staffer's actions in handing the report to French authorities "constitutes a serious breach of protocol, which, as is well known to all OHCHR officials, requires redaction of any information that could endanger victims, witnesses and investigators."
The staffer has been suspended with full pay while an investigation is carried out into the OHCHR's handling of the matter, the statement said.
"Our preliminary assessment is that such conduct does not constitute whistleblowing."
About 2,000 French soldiers are in the Central African Republic, according to the French Defense Ministry, alongside some 6,000 troops deployed with the U.N. peacekeeping force.
The French operation was launched in December 2013 in a bid to restore stability to the landlocked nation in central Africa -- one of the world's poorest.
The country began its descent into chaos in March 2013 after a coalition of mostly Muslim rebels ousted President Francois Bozize. The former Seleka group was subsequently forced from power, but Christian and Muslim militias continued to battle for control. To counter attacks on Christian communities, the vigilante groups known as the Anti-balaka, which translates to "Anti-machete," fought back.
The violence prompted a humanitarian crisis, as hundreds of thousands of people fled their homes. Some sought refuge in neighboring countries, but many others remain internally displaced, living in makeshift camps.
A tentative political transition is underway, but simmering sectarian tensions continue to threaten many communities.
The United Nations warned in a news release
Monday that the Central African Republic is "quickly becoming the largest forgotten humanitarian crisis of our time," with some 60% of the population of 4.6 million still in need of aid, including nearly 900,000 people forcibly displaced by conflict.