The situation of physical and mental development in children The height, weight, chest index and BMI were lower in age groups under-6, between 6 and 10 and 11 - 14 years old in the group 19 of children having BLLs ≥ 10 µg / dl compared with the other group. In particular, the gap is likely to increase in the higher age groups (Table 3.6 - 3.9).