Picture books are for young children or beginning readers. They can either have just pictures, without words -- such as Raymond Briggs' "The Snowman" -- or have pictures with a small amount of text, like in "Where The Wild Things Are" by Maurice Sendak. Picture books often feature repetitive phrases, to help children who are learning to read. They can be any genre, and are classified solely by their format.
Fantasy books are any novel -- or "chapter book," as they are often referred to in children's literature -- that is based on fanciful or unrealistic events. Fantasy is widespread in children's literature. Popular topics include magic or the occult, paranormal events, science fiction, animal-based fantasy or unusual or parallel worlds, such as the world in J.R.R. Tolkien's "The Lord of the Rings" trilogy. Perhaps the most famous children's fantasy books of the late 20th and early 21st centuries are the Harry Potter novels.
Realistic children's literature can either be set in contemporary times or in the past. As the name suggests, the characters are realistic and the plot line follows something that could actually happen. Realistic fiction can either be mostly for entertainment, featuring mysteries, adventures, sports or humor, or can try to tackle sensitive issues, such as life and death, family problems, cultural diversity or mental or physical illness. Realistic historical fiction uses real events from the past as a basis for the story.
Traditional literature is the name given to any stories which originated orally and were later written down. These include some fairy tales, folk tales, myths, legends, epics and fables. Traditional literature stories can be found in books, but are the type of story that a parent may tell a child from memory. Some of the best known traditional literature stories include "The Tortoise and the Hare," "Cinderella," "Theseus and the Minotaur" and "Little Red Riding Hood."