Let’s start with a look at the recommended weight for children. Most doctors use Body Mass Index or this growth chart from the Centers for Disease Control and Prevention. A child who falls below the 5th percentile is considered underweight. For example:
A 6-year-old who weighs about 36 or 37 pounds is in the 5th percentile.
A 10-year-old who weighs 55 pounds falls into the 5th percentile.
At the 5th percentile, thresholds for girls and boys are mostly the same.
These numbers do not account for height. Your doctor can give you a better idea of where your child falls on these charts by including stature. If your child is underweight, talk to your doctor about your child’s overall health and nutrition. Look for any nutritional deficiencies (anemia, lacking calcium or vitamin D), medication side effects, or unhealthy behaviors that may cause your child to not gain weight. Genetics also play a role in being thin, and your child may simply have a higher-than-normal metabolism.