The three children who received the apparitions had been brought up in an atmosphere of genuine piety: Lucia dos Santos (ten years old) and her two younger cousins, Francisco and Jacinta. Together they tended the sheep and, with Lucy in charge, would often pray the Rosary kneeling in the open. In the summer of 1916, an Angel appeared to them several times and taught them a prayer to the Blessed Trinity.
On Sunday, May 13, 1917, toward noon, a flash of lightning drew the attention of the children, and they saw a brilliant figure appearing over the trees of the Cova da Iria. The "Lady" asked them to pray for the conversion of sinners and an end to the war and to come back every month, on the 13th.
On that day a celestial phenomenon also took place: the sun seemed to tumble from the sky and crash toward earth. The children had been forewarned of it as early as May 13, the first apparition. The large crowd (estimated at 30,000 by reporters) that had gathered around the children saw the phenomenon and came away astounded.
Official recognition of the "visions," which the children had at the Cova da Iria, came on October 13, 1930, when the bishop of Leiria - after long inquiry - authorized the cult of Our Lady of the Rosary at the site. The two younger children had died: Francisco (who saw the apparition but did not hear the words) on April 4, 1919, and his sister Jacinta on February 20, 1920. Sister Lucia died on February 13, 2005, at her Carmelite convent in Coimbra, Portugal, after a long illness.
— Excerpted from Dictionary of Mary, Catholic Book Publishing Company.