The story of a young migrant girl who drowned at sea was at the heart of Pope Francis' address to some 400 children who on Saturday had traveled to the Vatican from the southern Italian region of Calabria.

Speaking off the cuff to the children who had arrived by the "Treno per Bambini" – "Children's Train" – and who represented various religions, cultures, and ethnicities, the Pope asked them to come up with a name for the unknown girl.

"Let us think of this little girl: what was her name? I do not know: a little girl with no name," the pontiff said, according to Vatican Radio's translation. "Each of you give her the name you would like, each in his heart. She is in heaven, she is looking on us."

Pope Francis told the story of the little girl as it was recounted to him by a rescue worker who had attempted to save the child, only to succeed in saving her lifejacket.

"He brought me this jacket," the pontiff said, showing the life jacket to the children, "and with tears in his eyes he said to me, 'Father, I couldn't do it – there was a little girl on the waves, and I did all I could, but I couldn't save her: only her life vest was left.'"

"I do not (tell you this because I) want you to be sad, but (because) you are brave and you (should) know the truth: they are in danger –  many boys and girls, small children, men, women – they are in danger," he said.

The annual "Treno per Bambini," which brings a group of young boys and girls, is an initiative of the Pontifical Council of Culture. The theme of this year's event is "Carried by waves," which is meant to evoke the image of both danger and hope experienced by migrants, reports Vatican Radio.

Among the initiatives involved in the event are the John XXIII Association, and the "Quattrocanti" Children's Orchestra of Palermo, which brings together boys and girls of eight different ethnicities.

The principal of a school in Vibo Marina, Mary Salvia, brought with her to the At the May 28 event Vatican money which had been collected by the school for the children of Lesbos, along with a letter signed by her students.

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"We children promise that we will welcome anyone who arrives in our country," said the letter, which was read to Pope Francis by Cardinal Gianfranco Ravasi, president of the Pontifical Council for Culture: "we shall never consider anyone who has a different skin color, or who speaks a different language, or who professes a different religion from ours, a dangerous enemy."

During the Saturday afternoon encounter with the pontiff, one of the children asked what it means "to be Pope." He responded: ( do) the good that I can do."

"I feel that Jesus called me to this: Jesus wanted me to be a Christian, and a Christian must do (the good he can)," he said; "and Jesus also wanted me to be a priest, and a bishop – and a priest and a bishop must do (the good they can); I feel that Jesus is calling me to do this – that's what I feel."