As a result of the dramatic increase in the prevalence of overweight and obesity among children, childhood obesity is one of the most critical global public health challenges of the 21st century. Weight gain occurs when energy intake exceeds energy expenditure. Both genetic and environmental factors (such as a sedentary lifestyle) are implicated in its pathogenesis. Childhood obesity is associated with physical, psychological, and social consequences. Obese children are at higher risk of elevated fasting blood glucose, insulin resistance, impaired glucose tolerance, type 2 diabetes, hypertension, polycystic ovarian syndrome (PCOS), atherosclerosis and cardiovascular disease (CVD), sleep apnea, and asthma. Psychological and social consequences include low self-esteem, social discomfort and isolation, and depression. Since COVID-19 was declared a global pandemic, millions of children and adolescents worldwide have been affected drastically. While COVID-19 has increased the prevalence of weight gain and childhood obesity, obese children, on the other hand, have suffered excessively from COVID-19. Here, we provide details on the endocrine, metabolic, and epidemiological aspects of childhood obesity with a concise discussion of the relationship between COVID-19 and childhood obesity. The endocrine chapter is focused on childhood obesity pathophysiology and the role of adipocytes and insulin in the mechanism of obesity. The metabolic chapter covered metabolic diseases related to childhood obesity. In contrast, the epidemiological chapter covered the risk factors of childhood obesity and current approaches to the prevention of childhood obesity.