体质指数不适合计算儿童的适当体重。 体质指数不适合计算老年人和运动员的适当体重，因为它并未计入骨质密度、肌肉质量或脂肪比例。

I'm interested in that, but I only have a few mins. Can you give me at most the first 500 characters of a detailed explanation in English about that?
Assess the weight of children and teens by using a BMI Calculator specifically designed for younger age groups. The Children's BMI uses height and weight measurements, gender, date of birth and date of measurements to perform weight assessment calculations.  Children measuring at the 5th percentile or lower are deemed underweight.  Children measuring between the 5th and 84th percentile are considered at a healthy weight  Children measuring between the 85th and 94th percentile are deemed overweig