Platelets play a fundamental role in hemostasis; however, their phenotype, reactivity, and function vary across the pediatric age spectrum. While developmental differences in plasma coagulation proteins have been well-characterized in children, differences in platelet biology remain poorly understood, with most studies focused on neonates. Consequently, the understanding of normal platelet phenotype and function in healthy children remains limited, making it difficult to interpret platelet changes in the context of disease. Platelet phenotype evolves from birth through adolescence, with ongoing changes in receptor expression and granule content. Functional responses also change with age, with neonatal platelets being hyporeactive compared with adult platelets, whereas platelets from older children may demonstrate increased responsiveness to common agonists. These developmental differences are increasingly recognized as clinically relevant across a range of pediatric disease states. However, key knowledge gaps remain in age-specific reference ranges and the translation of platelet biology into clinical practice. This review summarizes the current evidence on developmental differences in platelet production, phenotype, and reactivity from birth to adolescence and examines their clinical significance in pediatric disease states.