This systematic review assessed the prevalence of restless sleep in children, documented the association of restless sleep with other conditions, and summarized the existing evidence regarding whether restless sleep should be considered a distinct sleep disorder. A comprehensive search of electronic databases was performed using the broad search term “restless sleep” in all fields. Of the 266 articles retrieved, 107 were retained for inclusion in this review. The majority (n = 93) were observational studies. The studies were grouped under several pathologic/condition categories: sleep-disordered breathing (n = 19); adenotonsillectomy (n = 7); respiratory disorders, otitis media, and smoke exposure (n = 12); sleep-related movement disorders and restless sleep disorder (n = 11); neurologic or psychiatric disorders (n = 7); Down syndrome/other neurodevelopmental disorders (n = 10); sleep-related bruxism and other sleep disorders (n = 7); and restless sleep in the general population/mixed clinical samples (n = 18). A high prevalence of restless sleep was found in children with many of these underlying conditions, likely related to associated inherent sleep disruption and frequent awakenings (e.g., apnea and periodic limb movements), pain, sleep instability, and caregiver perception. The majority of studies identified restless sleep as reported by the caregiver, only 34 studies attempted to define restless sleep further. Four studies provided supportive evidence for designating restless sleep as an independent sleep disorder, restless sleep disorder (RSD). This review highlights the fact that the prevalence, etiology and sequelae (including daytime impairments) of restless sleep in children are important topics deserving of further research and that clinical definitions based on empirical evidence need to be developed. The designation of “primary” versus “secondary” restless sleep may be a useful construct, especially with regard to developing clinical trials and treatment algorithms.