Abstract
<jats:p>This monograph reframes rising youth screen time not as a failure of individual self-control but as a structural transformation of childhood. It introduces the “digital cohort” to describe birth-year groups whose developmental trajectories unfold within historically specific technological environments, where screens move from optional tools to socially unavoidable infrastructures. Drawing on cohort theory and life-course epidemiology, the study analyzes how timing, dose, duration, and accumulated exposure shape youth well-being across nations. It traces the shift from scarce screens to ambient saturation, examines displacement of sleep, movement, play, and face-to-face contact, and identifies institutional lag in schools, healthcare, and families. The attention economy is treated as a macro-level force, with persuasive design and algorithmic amplification engineering compulsion. Extending bioecological theory to digital ecosystems, the monograph proposes precautionary, population-level responses that rebuild developmental time, protect low-bandwidth sociality, and distribute responsibility across platforms, governments, schools, researchers, and communities.</jats:p>