Childhood obesity is a medical condition where children weigh more than expected according to their age and height. It is caused by genetics, lack of physical activity, unhealthy eating habits, and medical or psychological conditions. Complications include type 2 diabetes, high cholesterol, high blood pressure, bullying, learning problems, and depression. Prevention involves limiting sugary drinks and eating outside food, providing fruits and vegetables, encouraging physical activity, limiting screen time, ensuring enough sleep, and making healthier choices.