Two of the three children who reported seeing the Fatima apparitions died within two years of each other as children themselves, and the Church took decades to decide what to do with what they had said.
Three children, two early deaths
The visionaries, cousins Lucia dos Santos, Jacinta and Francisco Marto, reported the apparitions in 1917 while all under the age of eleven. Jacinta and Francisco both died in the 1918 to 1919 influenza pandemic while still children, and only Lucia lived to adulthood, becoming a nun and continuing to describe and clarify the reported messages for decades until her death in 2005.
A slow, formal process
The Catholic Church did not rush to a verdict: the local bishop declared the apparitions worthy of belief only in 1930, thirteen years after the events, and Jacinta and Francisco were not beatified until 2000, with their formal canonisation following considerably later still, a pace reflecting the Church's generally cautious, multi-stage approach to approving reported private revelations rather than any doubt specific to Fatima.
As this entry's companion article covers
The Miracle of the Sun witnessed by a large crowd in October 1917, and the specific content of the so-called Three Secrets of Fatima, are addressed directly in this entry's companion article rather than repeated here.