Index.of Feet Is This Really Bad??????

Is this really bad?????? - index.of feet

Since I was a child BMI calculator for children.
He says ... All information is given.

After 12 years and 11 months (female) child
is the £ 85.4
and 5 feet 3 inches is large
a BMI of 15.2,
item 5 under Percentile

and show that your child is underweight.

Is it really bad?

Thank you.