In 1952, the real Lúcia, the last surviving Fátima visionary, saw the movie and said that she did not like it.
The principal character in the movie aside from the children, Hugo da Silva, their agnostic, fortune-hunting but lovable friend played by Gilbert Roland, was a fictional person, introduced to soften the impact of a sectarian movie on the wider public. He does not appear in "La Señora de Fátima," the 1951 black-and-white Spanish film version of the story made just prior to this one.
Rather than letting Susan Whitney speak her own lines in the final scene, when she appears with stage makeup to age her appearance so as to appear as Lucia did at age 47, the filmmakers dubbed in the very recognizable voice of Angela Clarke who also dubs the Virgin Mary.
On May 13, 2017, exactly a century after the three children first saw the Lady, Pope Francis canonized Jacinta and Francisco Marto. The children are now venerated as the youngest non-martyred saints of the Roman Catholic Church. Lucia, who died in 2005, bears the title Servant of God, the first step to being recognized as a Saint.
Max Steiner (who was Jewish), composed the film's Oscar-nominated musical score. He accomplished this in part by researching Catholic hymns to the Blessed Virgin Mary and discovering a similar musical construct in some of them, which he then employed in the theme music.