Children's books must primarily be appropriate for children so that they could be a significant stimulus in children's lives. In other words, it is essential that the concepts child reality, literary criteria and artist sensitivity be reflected in books in order to create children's books. From birth to age 6, the fact that children's books are written in such a standpoint can help children in this age range have love and habit of reading. In this respect, this article proposes that children's books from birth to age 6 be written primarily according to the principle of appropriateness for children. With this respect, firstly, the conceptual framework of the principle of appropriateness was established through scientific evidence, and then this principle was reflected in the design, contextual and didactic attributes of children's books from birth to age 6. While forming this conception, birth-24 months, 24-48 months and 48-64 months age groups which Piaget adopted in Cognitive Theory were prioritized. Thus, an approach to write and publish books appropriate for children of these age groups and in different development levels has been developed.