On her last visit, a crowd of 70,000 people (including, the story goes, members of the sceptical, anti-religious press) witnessed the great Miracle of Fatima: the sun began dancing around in the sky and went completely dark for several minutes before returning to its proper place.
Most of the interest in Fatima, however, revolves around the famous Three Secrets of Fatima, which include remarkable visions of the future. Two secrets have been made public. The first described a horrific vision of Hell, while the second foretold the end of World War I, the beginning of World War II and called for the "Consecration of the Sacred Heart of Russia." Many believe Pope John Paul II fulfilled this request by giving a blessing over Russia shortly before the collapse of the Soviet Union.
The third secret was kept under wraps by the Vatican until Easter 2000 -- despite the Virgin's declaration that it should be released to the public in 1960. This naturally led to much speculation over its contents; many believed it concerns either corruption within the church or else contains details of an assassination plot against the pope. The secret was actually a message concerning the assassination of the Pope and the conversion of Russia.
Of the three children, siblings Francisco and Jacinta Martos and their cousin Lucia dos Santos, only Lucia is still alive. She lives in the convent of the Carmelite Sisters of Coimbra, which she first entered in 1928. Francisco and Jacinta Martos both perished in the Great Spanish Flu Epidemic of 1919, and were declared "venerable" (two steps away from sainthood) in 1989. (See Canonization for more on that process.)
-- [ (http://www.vatican.va/roman_curia/congregations/cfaith/documents/rc_con_cfaith_doc_20000626_message-fatima_en)] - Official Vatican Statement releasing the third secret of Fatima