The BMI calculator for adults does not distinguish between age and gender, which are crucial parameters for growth assessment in children. In adulthood, only single limits for overweight (BMI 25) and obesity (BMI 30) are used. For childhood and adolescence, which are characterized by dynamic development, it is necessary to use percentile methods.
The thresholds for childhood obesity are lower than for adults, and therefore, if the child exceeds a BMI of 30, then it is almost certainly obese.