Francisco and Jacinta Marto were the youngest two children of Manuel and Olímpia Marto, peasant shepherds of the hamlet of Aljustrel in the Cova da Iria pasturage of central Portugal. Their elder cousin Lúcia dos Santos lived in the next-door cottage. On May 13, 1917 — during the World War I year that also saw the Russian Revolution — the three children, while pasturing sheep at the Cova da Iria a half-hour walk from Aljustrel, experienced the first of six monthly apparitions of the Virgin Mary.
The apparitions ran May 13, June 13, July 13, August 19 (delayed by the children's arrest by the anti-Catholic Republican Portuguese authorities), September 13, and October 13, 1917 — the last accompanied by the public Miracle of the Sun witnessed by an estimated 70,000 onlookers, in which the sun appeared to dance, spin, and approach the earth in the cloudless sky over Fátima. The Virgin entrusted the children with the message that came to be called the 'Three Secrets of Fátima' — the vision of hell (revealed 1917), the prophecy of the rise and conversion of Russia to be obtained through the consecration of Russia to the Immaculate Heart (revealed 1942), and the third secret revealed only in 2000 (the vision of a 'Bishop dressed in White' being shot — interpreted by Pope John Paul II as the foreshadowing of the 1981 assassination attempt against him).
Francisco and Jacinta died young as the Virgin had foretold: Francisco of the Spanish influenza (1918 pandemic) on April 4, 1919 at ten; Jacinta of a tuberculosis-related sequela of the same influenza in Lisbon on February 20, 1920 at nine. Their cousin Lúcia (1907–2005, who lived as a Discalced Carmelite at Coimbra until age 97) was preserved alive to communicate the messages and the Secrets through the 20th century. Beatified together at Fátima by John Paul II in 2000 on the 83rd anniversary of the third apparition; canonized together at Fátima on the centenary of the first apparition (May 13, 2017) by Pope Francis. They are the youngest non-martyred saints in the Roman Catholic calendar.