These three made a huge impression on me starting when I was seven or eight through about eleven or so - I was a precocious reader, but they were topics of serious interest to me! In those days I thought I would be a primatologist when I grew up. Only later did I realize that the most interesting and complex primate is the human being...
1. Jane Goodall, In the Shadow of Man. I read it again and again, and knew the chimpanzee genealogies by heart.
2. Harlan Lane, The Wild Boy of Aveyron. The discussions of language in this book burst upon me like an explosion.
3. Donald Johanson and Maitland Edey, Lucy: The Beginnings of Humankind.
Other influential books at this age, excluding fiction: the D'Aulaires' books of Greek and Norse myths; David Macaulay's castle and cathedral books.