Certainly as writers you have thought about the many ways that characters can be created.
Have you thought of the ways that real people may be models of fictional characters, or how fictional characters (completely or partially)(exactly or the opposite) may be based on real people?
Take a look at the Web sites cited below for information about two famous children's stories' characters and the real people they are based on:
Find out about Alice Liddell (the girl who was the basis for the Alice of the "Alice in Wonderland" and Alice Through the Lookinglass" books by Lewis Carroll (aka Lewis Dodgson) http://www.pancakeparlour.com/Wonderland/Wonderland/Alice_Liddell/From8to80/from8to80.html
and www.marktwainmuseum.org/content/research/faq.php (scroll to question about Mark Twain's characters: Tom Sawyer, Becky Thatcher, and Huck Finn)
Now think of someone you know, or traits of a few people you know, and write a paragraph that creatively paints a portrait in words of a young character for what could become one of your stories for children or teens.