Pediatric nutrition must support rapid growth, brain development, and immune system maturation across developmental stages. Infants require 100-120 kcal/kg/day with breast milk or iron-fortified formula as the sole nutrition source for the first 6 months. Breast milk provides optimal nutrition with immunoglobulins (especially IgA), lactoferrin, and prebiotics that protect against infections. Introduction of solid foods begins at approximately 6 months when developmental readiness signs appear (sitting with support, loss of tongue thrust reflex, interest in food). Toddlers (1-3 years) need approximately 1,000-1,400 calories daily with a variety of foods from all food groups. Iron deficiency is the most common nutritional deficiency in children, particularly in toddlers who drink excessive cow's milk displacing iron-rich foods. Calcium and vitamin D requirements increase during adolescent growth spurts to support bone mineralization.