As the boy is directed to shoot, presumably, his father he is handed a semi-automatic hand gun. The camera closes in on the gun and you can see the hammer is cocked, but when he pulls the trigger the hammer closes, there is a flash from the nozzle and a boom, however, the slide doesn't move, nor is the shell ejected.
The cap gun with which the children are playing has an orange tip. Cap guns did not get these until 1992 when the Department Of Commerce prohibited the manufacture, shipping, or sale of toy guns unless they had orange tips. This was designed to ensure that police did not think that these toys were real guns and inadvertently end up shooting children. As the setting is 1950, these toys are out of place.