In the movie, Scout, Jem, and Dill at first view Boo Radley as a curiosity, even a freak, and are interested only at getting a peek of him. At the same time, the children are also afraid of Boo, mainly because they were told he tried to murder...
his parents with a knife. These perceptions are best illustrated in the scene where the children sneak into the Radley's yard through the garden to spy on Boo and then flee in terror, with Jem actually losing his pants on the wire fence when they think Boo is about to get them.
As the movie moves through the plot line of Tom Robinson's trial the children lose interest in Boo as they focus on Atticus' defense of Robinson and the actions of some of the town's residents. Despite the fact that he is innocent, Robinson is eventually found guilty of rape and is killed by the sheriff's deputy while trying to escape. Life then returns to normal in Maycomb and Dill returns home.
By the movie's climax Boo becomes something entirely different in the eyes of Scout. Boo becomes their savior when he rescues Scout and Jem from the clutches of Bob Ewell. As the grownup Scout narrates in the movie, "He gave us two soap dolls, a broken watch and chain, a knife, and our lives." Interestingly, Jem's perception may not have changed, at least not by the movie's end, as he was knocked out by Bob Ewell and does not yet realize he and Scout were saved by Boo.