That's unfortunately a question that's hard to give a simple, specific answer to without seeing the child or knowing his/her gender, height, weight, build, and frequency of physical activity. The amount of calories we need in a day is dependent on a lot of different variables.
For an "average" 12-yr-old male of 88 pounds, he will likely need about 2,000-2,200 calories per day. For an "average" 12-yr-old female of 90 pounds, she will likely need 1,800-2,000 calories per day.
A very good estimate that I have found useful that considers many of these factors is the "My Pyramid Plan" at www.mypyramid.gov. You can put in the age, gender, weight, height, and physical activity level to get a report of how many estimated calories are needed daily and how they should be divided among the food groups. You can then save or print the colorful, user-friendly reports. This works for children and adults alike and is neat because you can enter new information as the child grows and it provides a great explanation of the food groups and appropriate serving sizes.
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