Book excerpt: Despite the fact that the risk of childhood disease is lower now than it has been in the past, childhood health care needs remain complex. This is mainly because as society and technology change rapidly, children are routinely exposed to new potential threats. For instance, in the last few years the National Institutes of Health and the Surgeon General have been warning of an epidemic of childhood obesity in the United States, resulting from lack of exercise and poor nutrition. Children are not small adults, and their bodies react differently to toxins, invading viruses, and medications. Their swiftly changing metabolisms and immature immune systems require specialized attention and conscientious preventive measures such as vaccination. The Encyclopedia of Children's Health and Wellness is a two-volume set offering more than 600 entries covering all the key aspects of childhood health from infancy to age 18. Explaining diseases, conditions, general health, safety issues, learning, growth and development, medications, treatments, and much more, this encyclopedia is a comprehensive reference to the health issues facing children today. Completing this invaluable reference is a series of appendixes providing resources, organizations specializing in major childhood diseases, hotlines, useful books, a glossary, a guide to choosing a pediatrician, and much more.