Pediatrics is a branch of medicine concerned with children’s physical, mental, and psychosocial health. We have recognized for centuries that children are not just “little adults” with respect to their unique developmental trajectories, disease conditions, and drug-/small molecule-based and device-based therapies. This introduction to the history of child health serves as the backdrop to this volume on pediatric engineering. The chapter starts with the historical evolution of clinical pediatrics and its inexorable subspecialization as the body of knowledge and therapeutic approaches grew. Next, we interweave several illustrative examples of why “children are not just little adults”: The special cases of the developing human being and newborn infant; the dawn of pediatric surgery; pharmacokinetics and pharmacodynamics in children; and allometry, the complex science of size and scaling. The need for tailored therapy in the pediatric population further illustrates how children are distinct from adults, including their medical treatments, surgical and procedural interventions, and devices; pediatric public health and social engineering; and gene therapy. Then, we touch on how early life events—in both health and disease—can cast ripples decades later: the developmental origins of adult disease. Finally, despite the many advances specific to children’s health, disease, and treatment, we also take some lessons from occasions when pediatrics has failed children. Much work remains to be done to optimize the long-term health and well-being of all individuals within the pediatric-age population, but we are now at an exciting point in the history of pediatrics to start seeing truly tailored and individually engineered therapies for children of all ages, starting even before birth.