Background/Objectives: Sleep-Disordered Breathing (SDB) in children is closely associated with craniofacial growth and orthodontic conditions. Early identification of SDB risk in orthodontic populations is crucial, yet evidence remains fragmented. This systematic review aimed to summarize the prevalence of high SDB risk in pediatric orthodontic patients assessed through validated questionnaires. Methods: A systematic search was conducted across PubMed, Scopus, Web of Science, Cochrane Library and Embase following PRISMA guidelines. Inclusion criteria comprised analytical cross-sectional studies assessing SDB risk in children undergoing or seeking orthodontic treatment, using validated questionnaires such as the Pediatric Sleep Questionnaire (PSQ), OSA-18, or Sleep Clinical Record (SCR). The methodological quality of the included studies was assessed using the “JBI Critical Appraisal Checklist for Studies Reporting Prevalence Data”. The certainty of the evidence was additionally evaluated using the GRADE approach. Results: Twelve studies published between 2011 and 2025 met the inclusion criteria, totaling 3737 participants. Across studies, the mean prevalence of high SDB risk ranged from a minimum of 1.2% to a maximum of 69%, with consistently higher values in populations exhibiting malocclusions, oral breathing patterns, or craniofacial risk markers. All studies clearly described their populations and used validated screening tools, resulting in moderate overall quality. Conclusions: Pediatric orthodontic populations demonstrate a substantial prevalence of high SDB risk, suggesting that orthodontists should systematically incorporate validated questionnaires into routine screening. The evidence base, although consistent, remains limited by methodological weaknesses. Further well-designed studies are needed to clarify causal relationships between craniofacial development and SDB.