Background and objectives: Despite recognised disparities in child health outcomes associated with sleep, the majority of research has been based on small, homogeneous samples. Using a nationally-representative sample of US children and adolescents, we examined trends and social determinants of inadequate sleep across age groups. Study design: Comparison of cross-sectional studies. Methods: Our study used the 2003 (n = 68,418), 2007 (n = 63,442), and 2011/2012 (n = 65,130) waves of the National Survey of Children's Health, a nationally-representative survey of 6-17-year-olds. Parents reported whether the child had inadequate sleep (0-6 days of not getting enough sleep vs 7 days). Results: From 2003 through 2011/12, inadequate sleep increased from 23 to 36% among 6-9-year-olds, 30 to 41% among 10-13-year-olds, and 41 to 49% among 14-17-year-olds. Among 10-17-year-olds, those from households with more than a high school degree were more likely to have inadequate sleep (adjusted ORs 1.2). Although for 10-13-year-olds there was a gradient in inadequate sleep across income (aORs 1.2-1.3), for 14-17-year-olds, only those from the two highest income levels were more likely to have inadequate sleep (aORs 1.3-1.4). Parents' reports that neighbours did not watch out for other's children was associated with an increased risk for inadequate sleep across all ages (aORs 1.1-1.3). Conclusions: Inadequate sleep occurred as young as age six years and increased with age, became more prevalent, and was socially patterned. In order to prevent inadequate sleep across the life course, surveillance and monitoring are needed across all age groups to identify critical periods for intervention. (C) 2016 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.