Diets that severely restrict food choices, calories, and/or fat are not recommended for children. These diets may lack nutrients needed for normal growth and development. Discuss this issue with your pediatrician. For growing children it is often safest to maintain their current weight gain while they grow in height rather that try to lose weight.
The best way for most children to do this is to become more physically active rather that significantly restrict calorie intake. You can help by limiting your child's total "screen" time (TV and computer) to 1-2 hours each day. Also, make sure your child eats at the table, not in front of the TV or wandering through the kitchen, where little attention is paid to the amount of food being eaten. Serving meals and snacks at regular times will also help curb overeating.