If your daily caloric requirement is 2000 calories, you could only lose two pounds a week if you were on a 1000 calorie per day diet. Suppose your daily caloric requirement is 1200 calories. When you consider the numbers you have to agree that diets that promise 20 or 30 pounds of weight loss in a few weeks can't result in a true fat loss of so many pounds. There are factors which can effect caloric expenditure. The most important is exercise.
Studies show that obese children naturally conserve energy.
If you watch a group of children playing baseball, you will notice that the slim children are in motion most of the time while the overweight children tend to stand still until the ball comes their way. While at least 20 minutes of vigorous exercise every day is good habit to develop since it is good for the heart and will benefit weight control, just as we saw that small amounts of calories can add up, so can small amounts of activity. The best thing we can do for overweight children is to get them up and moving. This means getting them away from the TV where they are sedentary and also more likely to consume extra snacks. Team sports provide many advantages to children, but many obese children can't compete and end up warming the bench.