The United States Centers for Disease Control and Prevention, or CDC, and the Baylor College of Medicine are online sources that provide charts of body mass index, or BMI, for young children and teens up to age 20. Both sources also have BMI calculators so that parents can input data, such as the child's birth date, gender, height and weight. This information is needed to make a BMI calculation and then use the chart to interpret if a child has a normal BMI for his age and gender or not.
The BMI is a calculation utilized to approximate the amount of body fat a person has. It is a method used by doctors to determine if the child's age, weight and height are appropriate. When looking at these charts, which can be given based on gender, a percentile ranking is also given. A percentile ranking refers to how a child compares to other children who are of the same age and gender, relates WebMD. For example, an 11-year-old boy, who has a BMI of 25, is considered obese and is in the 95th percentile range, according to the chart provided by the CDC.