This is really all about your story being logical.
The question “Why?” is very useful here. “How?” is also quite enlightening. If you could read your work backwards it might be helpful. Why is the gun smoking? How did it get there? Why has the father written this letter? How was it delivered? Why did the boy steal the loaf? How did he manage that?
Does every happening lead to something else? Every scene must have its consequences. It’s useful too if it projects forward. What will that gun do? What will the protagonist do because they have received the letter? What will now happen to the boy who stole the loaf?
Can that really have happened? We looked at this with endings. Something must happen. It mustn’t be too melodramatic. You mustn’t cheat and have some unbelievable magic move you on too easily. Don’t find the gun conveniently hidden in the chimney. Don’t let the letter contain a magic formula for curing all the protagonist’s ills. Don’t make the boy the secret love child of the judge. (Though we may have to forgive Dickens, Molière and Shkespeare for such tricks).
How to proceed with this
Examine every scene carefully and ask these four questions.
What has caused this to happen?
What will this lead to?
Is the relationship between cause and effect believable?
Does this scene actually add to the story?