Insufficient sleep is associated with poor health and increased mortality. Studies on whether parenthood (including consideration of number and ages of children) is associated with sleep duration or sleep problems are scant and inconclusive. Using data collected in the Wisconsin Sleep Cohort Study (n = 4,809) between 1989 and 2008, we examined cross-sectional associations of number and ages of children with self-reported parental sleep duration, daytime sleepiness, and dozing among employed adults. Longitudinal change in sleep duration over 19 years was examined to evaluate changes in parental sleep associated with children transitioning into adulthood (n = 833). Each child under age 2 years was associated with 13 fewer minutes of parental sleep per day (95% confidence interval (CI): 5, 21); each child aged 2-5 years was associated with 9 fewer minutes of sleep (95% CI: 5, 13); and each child aged 6-18 years was associated with 4 fewer minutes (95% CI: 2, 6). Adult children were not associated with shorter parental sleep duration. Parents of children over age 2 years were significantly more likely to experience daytime sleepiness and dozing during daytime activities. Parents of minor children at baseline had significantly greater increases in sleep duration over 19 years of follow-up. Parenting minor children is associated with shorter sleep duration. As children age into adulthood, the sleep duration of parents with more children approaches that of parents with fewer children.