Sometimes a book is referred to as a middle grade novel or as a picture book. What is the difference between the two? What age groups do they cover? Following are general age guidelines. These age guidelines have been modified over the years and will probably be modified in the future. Plus some of the groups overlap each other.
Picture Books - Ages 0-4. Picture books are usually around 32 pages in length and the amount of text is usually one or just a few sentences per page. There are also "board" books which are made of thick board. They are made of this material because they are for infants and can better weather how an infant may physically handle a book.
Chapter Books or Early Readers - Ages 5-8. Chapter books have short chapters that are specifically designed for emerging young readers.
Middle Grade - Ages 7-10 and Ages 8-12. Sometimes there are "lower middle grade (ages 7-9) and "upper middle grade" (Ages 10-13). The average length of a middle grade novel is 20,000 words or 100 pages.
Young Adult or Teens - Ages 13-18. This area has a great range of topics. Some of the books in this category mimic adult books and are geared for 17-18 year olds. This category is often not placed within the children's section at the bookstore, but is closer to the regular adult section.