During the 1913–1920 window, pediatrics coalesced around infant metabolism, nutrition, and growth—integrating fat metabolism, gut permeability, gastric secretion at birth, and feeding strategies to illuminate energy balance in early life. The clinical spectrum broadened to neonatal diseases and prognosis, while developmental biology and early diagnostic tools enhanced the ability to detect embryonic and neonatal anomalies. Hematology and immunology matured rapidly, and studies of neonatal oncology and metabolic pathology linked early-life biology to broader disease processes. Historical Significance: Historians of pediatrics view this era as a turning point where nutrition, metabolism, and immune development in infancy were integrated into a coherent scientific program, with practice patterns and diagnostic concepts laid down for neonatal care. The emergence of neonatal coagulation testing, immunohematology, and early recognition of developmental brain disorders seeded later subspecialties in child neurology, allergy, and pediatric oncology. By translating laboratory insights into clinical practice, the period anchored modernization of pediatric care and influenced research directions for decades to follow.