Full-color, fun, and crammed with cool facts, DK's Secret Worlds Series takes a fresh look at familiar subjects with brilliant results Kids ages 9 and up can delve into a wide range of subjects from nature, history, and science for researching school projects, satisfying a curious appetite, or just for the love of reading. Tried-and-tested web sites and a mega-reference section are just two of the innovative features that will keep kids and parents coming back for more.