Childhood obesity is a key public health issue in the United States and around the globe in developed and developing countries. Obese children are at increased risk of acute medical illnesses and chronic diseases—in particular, osteoarthritis, diabetes mellitus, and cardiovascular disease, which can lead to poor quality of life; increased personal and financial burden to individuals, families, and society; and shortened lifespan. Physical inactivity and sedentary lifestyle are associated with being overweight in children and adults. Thus it is imperative to consider exercise and physical activity as a means to prevent and combat the childhood obesity epidemic. Familiarity with definitions of weight status in children and health outcomes like metabolic syndrome is crucial in understanding the literature on childhood obesity. Exercise and physical activity play a role in weight from the prenatal through adolescent time frame. A child’s family and community impact access to adequate physical activity, and further study of these upstream issues is warranted. Recommended levels of physical activity for childhood obesity prevention are being developed.