The narrator opened the scene at Fatima saying, "Here we are in the mountain village of Fatima on Sunday, May 15, 1917". That Sunday was on the 13th of the month, and the lady asked the children to return for six months in succession on the 13th day to the Cova da Iria, as the movie itself indicates.
Just before the first vision occurs, Sherry Jackson picks up a little lamb, and holds it all the way through the vision. Frontal shots (from the lady's POV, showing the kids looking up) show her holding an actual lamb. Shots from the rear (showing the three children before the bush with the lady on it) show Sherry holding an obvious wooden or plastic model.
The Lady told Lucia to learn how to read and write so she could spread God's message. When the administrator took them away in his car, Lucia was able to read a signpost indicating that they were going to the next town.