Interstitial lung diseases (ILDs) occur across the lifespan, from birth to advanced age. However, the causes, clinical manifestations, histopathology, and management of ILD differ greatly among infants, older children, and adults. The historical approach of classifying childhood ILD (chILD) using adult classification schemes may therefore have done more harm than good. Nevertheless, identification of novel forms of chILD in the past decade, such as surfactant metabolism dysfunction disorders and neuroendocrine cell hyperplasia of infancy (NEHI), as well as genomic analysis of adult ILDs, has taught us that identical genotypes may result in distinct phenotypes at different ages and developmental stages, and that lung developmental pathways and cellular phenotypes are often recapitulated in adult ILDs. Thus comparison of the pathophysiology of ILD in children and adults in the context of lung development is useful in understanding the pathogenesis of these disorders, and may lead to novel therapeutic interventions for ILDs at all ages.