The 6-12 year age group is in a latent period of growth, while children 12-18 years old experience their main period of growth. The usual BMI range is 18 to 23. But is it applicable to children who are 6 to 12 years old?

Sometimes with higher income groups I also find children with lower BMI scores - for example, 13. Sometimes children do not show any significant symptoms, or they have low haemoglobin counts in blood tests. And childhood obesity is becoming more common. So is it useful to take BMI into consideration to determine a balanced diet for a child of this age group? What BMI range should be considered as optimum for children below 12?