I want to write a story about a segregated city with a river a border between the two sides -> a black girl and a white boy become friends when they both come to the river... they make a pretend "world" together.
When the girl tells her friends about the world, her friends don't believe her not because the world doesn't exist, but because people don't think that a black and a white kid can be friends.
This is to answer the prompt "write about a favorite memory that did not actually happen." Does it fit the prompt well? If so, can someone tell me how to write the tone and mood of the story?