The Yellow Balloon (1953)

One of two young boys accidentally falls to his death while playing in a bombed-out London neighborhood. Frankie, the survivor, feels guilty about his friend's death. Len, a petty thief who has just killed a pub owner during a botched robbery, learns of the accident. Posing as Frankie's friend, he blackmails the boy into stealing from his parents to finance his escape. After Len decides that Frankie might know enough to connect him with the murder, he decides to silence him in a tense hide-and-seek chase through the ruins.