Pediatrics is the branch of medicine that deals with the medical care of infants and children.
One of the major challenges facing pediatricians is that the range of body sizes (and weights) that they face in pediatrics is much greater than in adult medicine. For example, a preterm neonate can be less than 2kg in weight while an obese adolescent may be larger than the typical adult.
Childhood is the period of greatest growth, development and maturation of the various organ systems in the body. Years of training and experience (above and beyond basic medical training) goes into recognizing the difference between normal, normal variants and what is actually pathological.
Another major difference between pediatrics and adult medicine is that children are minors and, in most jurisdictions, cannot make decisions for themselves. The issue of guardianship, legal responsibility and informed consent must always be considered in every pediatric procedure. In a sense, pediatricians often have to treat the parents (and sometimes, the family), not just the child.