Dr. Greene's Answer
A child is failing to thrive when she is not growing at the expected rate for her age, or if her weight is disproportionately low compared to her height and head circumference.
A simplistic but very useful way to look at growth failure is to consider that in order to grow, a child must take in adequate calories, absorb those calories, and use them for growth.
If a child is not growing well, first consider whether she is actually taking in an adequate number of calories (and other nutrients). What is she being fed? How much is offered and how often? How much does she actually take? Is she able to suck and swallow adequately? Most cases of failure to thrive in infants can be solved by carefully addressing these questions. But sometimes problems, calories loss, or calorie usage are the root causes of failure to thrive.
Some children will even fail to thrive in the face of adequate calorie intake and absorption simply from extreme neglect. Kids who are not hugged, held, and cared for don’t grow. This has been clearly demonstrated in orphanages where the adult-child ratio is very low. Even if these children are being well nourished, they often fail to thrive, simply because they lack personal care.