How do you interpret the title of the story?
If you knew nothing about the book, other than the title, how would you interpret it? "Prison" sounds closed, dark, regimented, disciplined, monotonous, restrictive and isn't a place you'd like to be.
Then, as you read the book, you find out that the setting of the book is actually a candy store. Candy stores could be described as fun, bright, spontaneous, a treat, for children, happy places. The title and the setting are therefore in direct contrast.
Would you have guessed that the book was about a family working in a candy store from the title?
For Tony, the store is a prison. He's stuck doing twelve-hour shifts, with little personal time (an hour in the afternoon, in which he naps). There's no possibility of 'escape'. There are other hints of 'prison life': Rosa gives Tony a new name (Tommy), just like prisoners being referred to by an ID number.
There are references to petty, and more serious, crimes that occur during the novel.