How does a 12-year-old lose leg fat?

Your body is one organism so you can't talk about losing fat in only one part of it. Exercise and diet are both necessary. Your legs are especially difficult because unless you are bed bound, you are using them every day, so the muscles should be in good shape. You can increase exercises that just work your legs like lunges and bicycles, but you will also need to cut back on fat-making foods like sugars and other carbs. If you do a lot of just leg exercises, you run the risk of building up thigh muscle which is even harder to lose than fat. Power walking and other common exercises that stretch and strengthen all or most muscles will help you lose body fat without building up muscles in just one part of your body. Women usually need to develop upper body strength so exercising arms, shoulders and the upper back will help you burn calories.