I really hate to say this, but be a bit careful with kids who are in the low percentiles for weight around health professionals. My son and daughter were/are both thin and both in the lower percentiles for weight as children (when he was born, my son was in the 95th % for height and 5% for weight). One of the "well child" checkups for my daughter, the pediatrician decided she was too under weight. We were all stressed (in the midst of a divorce for years starting when she was 3). He made such a big deal out of it- I was obviously neglecting her- and sent her to counseling and a nutritionist. At 6. It added fodder to the divorce proceedings because I was obviously an unfit mother, and I could have lost custody. Now, at 27, she is still thin, but it's not my fault!