Here's a fun exercise that will help you practice your list-making skill and also get you started thinking about characters as well. Write a letter from a child at camp to his parents at home. Don't make it any random child; make it a famous person as a child. It can be a real person, such as Albert Einstein, Atilla the Hun, Moses, Abraham Lincoln, Donald Trump, or Bill Clinton, or it can be a fictional character like Sherlock Holmes, Santa Claus, or Dr. Frankenstein.
Start by making a list of everything you know about that person. For example, Abraham Lincoln:
He wore a stovepipe hat.
He had a beard.
He was assassinated by an actor.
He was president during the Civil War.
He wrote speeches on the backs of envelopes.
Now start thinking about how all these facts about the man would apply to Lincoln as a child. What if the Civil War is a camp colors war instead of a violent conflict? How does he get in the habit of writing things on envelopes? Is young John Wilkes Booth a camper at the nearby theater camp? Is his bunkmate a young General Grant? Did he make a hat out of an actual stovepipe for Funny Hat Day and the look just stuck?
You get the idea. You want to use the letter to hint at the person Lincoln would someday become.