As a part of a series of books written by physicians for their patients, this publication explains heredity, birth, and growth patterns to pre-teen children. The chapters are written in language appropriate for children moving from childhood into their teens and deal with topics like: cells, conception, prenatal development, puberty, and changing attitudes in the process of sexual maturation. Accompanying this book for pre-teens is a short publication for parents, "Your Child From 9-to-12," that discusses physical development in this age group, sex education goals, and approaches to imparting information. (ST)