The youngest writer known today was eight year old Jason Gaes. He was diagnosed with Burkitt's lymphoma at six, and given a 1 in 5 chance of survival. Jason felt there should be a book about childhood cancer, telling young people they didn't have to die. His book was put on the best seller list as a national outlook on life.
The book was soon turned into a movie called You don't have to die. It was a huge hit and was called a "You Don't Have to Die is a 1988 short documentary film directed by Malcolm Clarke and Bill Guttentag." by Wikipedia. The movie and book were also called "A young boy's successful battle against cancer and his subsequent efforts to help other children overcome their fears of the illness." by Internet Movie Data base.