If your child is below the 3rd or 5th percentile, but is growing normally with a growth curve that is parallel to the 3rd or 5th percentile, and he has a healthy diet and no associated symptoms, then your Pediatrician may just observe his weight gain over the next few months. If your child is not growing well, with a growth curve that is flat, moving downward across more than 2 major percentile or is moving further away from the 3rd or 5th percentile, then your Pediatrician may do further testing. Treatment of failure to thrive is usually carried out with a team approach, with your Pediatrician, a Pediatric nutritionist , and appropriate specialist referrals as indicated. There are many Pediatric specialists that can evaluate a child with failure to thrive, depending on your Pediatrician's suspicion of the cause. Often, especially if they have gastrointestinal symptoms, such as vomiting or chronic diarrhea, a Pediatric Gastroenterologist will evaluate your child.
Treatment depends on the underlying cause.
If no medical reason is found for your child's failure to thrive, then often treatment will consist of nutritional therapy to see if your child will gain weight if given an adequate amount of calories. This may be done in the hospital over a few weeks or it may begin as an outpatient. Turning meals into a power struggle usually doesn't help and may make your child more resistant to eating. Allow your child to feed himself, especially finger foods, as much as possible. Only offer liquids, especially juice, after the meal.