A main childhood task is learning. In this task, the role of sleep is increasingly demonstrated. Although most literature examining this role focuses on preadolescence and middle adolescence, some studies apply napping designs in preschoolers. Studies overall conclude that without proper sleep a child’s cognitive abilities suffer, but questions on how and to what extent linger. Observational studies show the hazards of potential confounders such as an individual’s resilience to poor sleep as well as developmental risk factors (eg, disorders, stressors). A better understanding of cognitive sleep neuroscience may have a big impact on pediatric sleep research and clinical applications.