An important part of managing diabetes in youth is finding the right energy balance. We want to make sure the child gets enough calories for growth but not so much that they gain a lot of weight. Physical activity also plays a role in how much energy is needed.
Energy needs depend on age, size, activity, and growth factors. Appetite is an important indicator of immediate calorie needs in children. Some children seem to eat more than they need, and some children may seem to eat less than they need.
High blood glucose levels can make all of these a challenge, where appetite might be very high or very low. A child with high blood glucose may not have much energy to go out and play, and may not be very hungry.
The equations listed below are often used by health professionals when figuring out how many calories are needed. These take into account age and gender as well as physical activity.
Estimated Energy Requirements for Children and Adolescents 

3 – 8 year 
88.5 – (61.9 x age [yrs]) + PA x (26.7 x weight [kg] + 903 x height [m]) + 20 kcal 135.3 – (30.8 x age [yrs]) + PA x (10.0 x weight [kg] + 934 x height [m]) + 20 kcal 
9 – 18 years 
88.5 – (61.9 x age [yrs]) + PA x (26.7 x weight [kg] + 903 x height [m]) + 25 kcal 135.3 – (30.8 x age [yrs]) + PA x (10.0 x weight [kg] + 934 x height [m]) + 25 kcal 
PA = physical activity coefficient 
if sedentary 
Another way to estimate the number of calories a child needs is to use these guidelines from the Joslin Diabetes Association.
Example
Let’s compare the two methods using an active 13 year old boy who is 5’6” (1.68 meters) and weighs 115 pounds (52.3 kilograms).
88.5 – (61.9 x age [yrs]) + PA x (26.7 x weight [kg] + 903 x height [m]) + 25 kcal = ?
88.5 – (61.9 x 13) + 1.26 x (26.7 x 52.3 + 903 x 1.68) + 25 kcal = ?
88.5 – (805) + 1.26 (1396) + 1517 + 25 = ?
88.5 – 805 + 1759 + 1517 + 25 = about 2500  2600 kcal
VS.
Joslin equation:
1000 calories + 100 (12) = 2200 calories
One is a little low, one is a little high. These equations only give an estimate of calorie needs. Remember, the amount of energy needed by a child or teen is usually dictated by their appetite. Growth is the best longterm indicator of the correct calories.