It's only a small grave, a rectangle of cheap concrete marking it out, blessed by a flourish of wild yellow lilies. Inside are the powdered bones and skulls and bits of femur of up to 300 children, Armenian orphans of the great 1915 genocide who died of cholera and starvation as the Turkish authorities tried to "Turkify" them in a converted Catholic college high above Beirut. But for once, it is the almost unknown story of the surviving 1,200 children – between three and 15 years old – who lived in the crowded dormitory of this ironically beautiful cut-stone school that proves that the Turks did indeed commit genocide against the Armenians in 1915.

Barack Obama and his pliant Secretary of State, Hillary Clinton – who are now campaigning so pitifully to prevent the US Congress acknowledging that the Ottoman Turkish massacre of 1.5 million Armenians was a genocide – should come here to this Lebanese hilltop village and hang their heads in shame. For this is a tragic, appalling tale of brutality against small and defenceless children whose families had already been murdered by Turkish forces at the height of the First World War, some of whom were to recall how they were forced to grind up and eat the skeletons of their dead fellow child orphans in order to survive starvation.

Jemal Pasha, one of the architects of the 1915 genocide, and – alas – Turkey's first feminist, Halide Edip Adivar, helped to run this orphanage of terror in which Armenian children were systematically deprived of their Armenian identity and given new Turkish names, forced to become Muslims and beaten savagely if they were heard to speak Armenian. The Antoura Lazarist college priests have recorded how its original Lazarist teachers were expelled by the Turks and how Jemal Pasha presented himself at the front door with his German bodyguard after a muezzin began calling for Muslim prayers once the statue of the Virgin Mary had been taken from the belfry.

Hitherto, the argument that Armenians suffered a genocide has rested on the deliberate nature of the slaughter. But Article II of the 1951 UN Convention on the Prevention and Punishment of the Crime of Genocide specifically states that the definition of genocide – "to destroy in whole or in part, a national, ethnical, racial or religious group" – includes "forcibly transferring children of the group to another group". This is exactly what the Turks did in Lebanon. Photographs still exist of hundreds of near-naked Armenian children performing physical exercises in the college grounds. One even shows Jemal Pasha standing on the steps in 1916, next to the young and beautiful Halide Adivar who – after some reluctance – agreed to run the orphanage.

Before he died in 1989, Karnig Panian – who was six years old when he arrived at Antoura in 1916 – recorded in Armenian how his own name was changed and how he was given a number, 551, as his identity. "At every sunset in the presence of over 1,000 orphans, when the Turkish flag was lowered, 'Long Live General Pasha!' was recited. That was the first part of the ceremony. Then it was time for punishment for the wrongdoers of the day. They beat us with the falakha [a rod used to beat the soles of the feet], and the top-rank punishment was for speaking Armenian."

Panian described how, after cruel treatment or through physical weakness, many children died. They were buried behind the old college chapel. "At night, the jackals and wild dogs would dig them up and throw their bones here and there ... at night, kids would run out to the nearby forest to get apples or any fruits they could find – and their feet would hit bones. They would take these bones back to their rooms and secretly grind them to make soup, or mix them with grain so they could eat them as there was not enough food at the orphanage. They were eating the bones of their dead friends."

Using college records, Emile Joppin, the head priest at the Lazarite Antoura college, wrote in the school's magazine in 1947 that "the Armenian orphans were Islamicised, circumcised and given new Arab or Turkish names. Their new names always kept the initials of the names in which they were baptised. Thus Haroutioun Nadjarian was given the name Hamed Nazih, Boghos Merdanian became Bekir Mohamed, to Sarkis Safarian was given the name Safouad Sulieman."

Lebanese-born Armenian-American electrical engineer Missak Kelechian researches Armenian history as a hobby and hunted down a privately printed and very rare 1918 report by an American Red Cross officer, Major Stephen Trowbridge, who arrived at the Antoura college after its liberation by British and French troops and who spoke to the surviving orphans. His much earlier account entirely supports that of Father Joppin's 1949 research.

"Every vestige, and as far as possible every memory, of the children's Armenian or Kurdish origin was to be done away with. Turkish names were assigned and the children were compelled to undergo the rites prescribed by Islamic law and tradition ... Not a word of Armenian or Kurdish was allowed. The teachers and overseers were carefully trained to impress Turkish ideas and customs upon the lives of the children and to catechize [sic] them regularly on ... the prestige of the Turkish race."

Halide Adivar, later to be lauded by The New York Times as "the Turkish Joan of Arc" – a description that Armenians obviously questioned – was born in Constantinople in 1884 and attended an American college in the Ottoman capital. She was twice married and wrote nine novels – even Trowbridge was to admit that she was "a lady of remarkable literary ability" – and served as a woman officer in Mustafa Ataturk's Turkish army of liberation after the First World War. She later lived in both Britain and France.

And it was Kelechian yet again who found Adivar's long-forgotten and self-serving memoirs, published in New York in 1926, in which she recalls how Jemal Pasha, commander of the Turkish 4th Army in Damascus, toured Antoura orphanage with her. "I said: 'You have been as good to Armenians as it is possible to be in these hard days. Why do you allow Armenian children to be called by Moslim [sic] names? It looks like turning the Armenians into Moslims, and history some day will revenge it on the coming generation of Turks.' 'You are an idealist,' he answered gravely and like all idealists lack a sense of reality ... This is a Moslem orphanage and only Moslem orphans are allowed.'" According to Adivar, Jemal Pasha said that he "cannot bear to see them die in the streets" and promised they would go "back to their people" after the war.

Adivar says she told the general that: "I will never have anything to do with such an orphanage" but claims that Jemal Pasha replied: "You will if you see them in misery and suffering, you will go to them and not think for a moment about their names and religion." Which is exactly what she did.

Later in the war, however, Adivar spoke to Talaat Pasha, the architect of the 20th century's first holocaust, and recalled how he almost lost his temper when discussing the Armenian "deportations" (as she put it), saying: "Look here, Halide ... I have a heart as good as yours, and it keeps me awake at night to think of the human suffering. But that is a personal thing, and I am here on this earth to think of my people and not of my sensibilities ... There was an equal number of Turks and Moslems massacred during the [1912] Balkan war, yet the world kept a criminal silence. I have the conviction that as long as a nation does the best for its own interests, and succeeds, the world admires it and thinks it moral. I am ready to die for what I have done, and I know that I shall die for it."

The suffering of which Talaat Pasha spoke so chillingly was all too evident to Trowbridge when he himself met the orphans of Antoura. Many had seen their parents murdered and their sisters raped. Levon, who came from Malgara, was driven from his home with his sisters aged 12 and 14. The girls were taken by Kurds – allied to the Turks – as "concubines" and the boy was tortured and starved, Trowbridge records. He was eventually forced by his captors into the Antoura orphanage.

Ten-year-old Takhouhi – her name means "queen" in Armenian and she was from a rich background – from Rodosto on the Sea of Marmara was put with her family on a freight train to Konia. Two of her two brothers died in the truck, both parents caught typhus – they died in the arms of Takhouhi and her oldest brother in Aleppo – and she was eventually taken from him by a Turkish officer, given the Muslim name of Muzeyyan and ended up in Antoura. When Trowbridge suggested that he would try to find someone in Rodosto and return her family's property to her, he said she replied: "I don't want any of those things if I cannot find my brother again." Her brother was later reported to have died in Damascus.

Trowbridge records many other tragedies from the children he found at Antoura, commenting acidly that Halide "and Djemal [sic] Pasha delighted in having their photographs taken on the steps of the orphanage ... posing as the leaders of Ottoman modernism. Did they realise what the outside world would think of those photographs?" According to Trowbridge's account, only 669 of the children finally survived, 456 of them Armenian, 184 of them Kurds, along with 29 Syrians. Talaat Pasha did indeed die for his sins. He was assassinated by an Armenian in Berlin in 1922 – his body was later returned to Turkey on the express orders of Adolf Hitler. Jemal Pasha was murdered in the Turkish town of Tiflis. Halide Edip Adivar lived in England until 1939 when she returned to Turkey, became a professor of English literature, was elected to the Turkish parliament and died in 1964 at the age of 80.