Archbishop Bernardito Auza, the Vatican's permanent observer to the United Nations, said: "Mary essentially came as an ambassador of peace with a summons for the shepherd children to be key staff members, to use U.N. jargon, of her permanent mission to all the nations."

The mission is "just as relevant today, with more than 50 active violent conflicts across the globe in what Pope Francis has called a 'third World War fought piecemeal,' as it was a century ago during the First World War," he said.

"It's astonishing that Mary would preferentially come, not to heads of state or diplomats or religious leaders directly to enlist them in the cause of peace but to three simple children without much education and entrust them with a message, secrets and a special task for the cause of peace and the good of souls and the world," Archbishop Auza said.

"The selection criteria shown by Mary reveals that everyone has a role, even those whom the world considers insignificant, or incapable or too young. If the shepherd children could be chosen, and they could respond as wholeheartedly as they did, it's a sign of what is possible for everyone," he said.

Archbishop Auza said the credibility of the Fatima apparitions to the children is beyond reproach and extends to the public miracle Oct. 13, 1917. On that day, gathered in anticipation of a promised sign from Mary, thousands of believers and skeptics saw the sun appear to "dance," spin and change colors.

He said it is unlikely that 70,000 people, including church authorities, journalists from anti-Catholic newspapers, unsympathetic pubic officials and anti-clerical people, experienced a mass hallucination with regard to the sun.

The message of Fatima encourages conversion from sins such as the idolatry of money, the burgeoning arms trade, and lack of hospitality to the needy migrants. "Without conversion, peace will always remain merely an illusion. Conversion is a precondition for peace," he said.

Peace begins in the heart, and prayer is its instrument, the archbishop said. "The message of Fatima contains a lesson about the objective value of prayer, that prayer can change not just the world inside the one praying, but the world outside," Archbishop Auza said.

Johnnette Benkovic, founder and president of Women of Grace, said Fatima's message is the hour has come when women impregnated with the spirit of the Gospel can aid humanity.

"Women have been entrusted with the totality of the human person and its protection" and an opportunity to help other women embrace their feminine genius and work for peace, Benkovic said.

Andrea Bartoli, dean of Seton Hall University's School of Diplomacy and International Relations in South Orange, New Jersey, said people must know the past and listen to one another, especially victims of conflict, to live in peace.

"In Fatima, the children were open to the possibility that life can be surprisingly peaceful," he said. People who want to hear the voice of God should listen with a humble heart educated by daily prayer, Bartoli said.

Marta Santos Pais, special representative of the U.N. secretary-general on violence against children, said by entrusting her message to very young, poor shepherds at a time of widespread destruction and hopelessness, Mary gave them a mandate of peacemaking. "Children of today have the same dream of a world where violence doesn't take place," yet for many children the dream is a nightmare, she said.

"Violence against children costs $7 trillion each year and compromises economies. It is a pervasive, corrosive and silent emergency that affects the world's youngest citizens, but it's not a fate," Santos Pais said. "Safe, inclusive, relevant, empowering, quality education can bring an end to violence," she said.

Anna Halpine, founder and CEO of World Youth Alliance, said the response of the shepherd children at Fatima is a model for all young people to follow. They offered their suffering and made prodigious spiritual growth as an extraordinary contribution to peace.

"The power of the powerless surprises us in every generation. By doing what is asked of us, we can do great things to build peace," Halpine said.

The event was co-sponsored by the Vatican's permanent observer U.N. mission and Portugal's permanent mission.