Oral mucositis (OM) is a prevalent acute adverse effect of various cancer treatments. Accurate assessment of OM is vital for effective prevention and treatment strategies. However, a lack of validated pediatric instruments for evaluating OM can lead to unreliable data, and hinder interventional and epidemiological research. This study aims to evaluate the methods used for assessing OM in pediatric oncology patients. A systematic review of four databases and a manual search yielded 113 articles. Nine different scales were identified, with the World Health Organization (WHO) scale being the most commonly used (61.9%). The Children's International Mucositis Evaluation Scale (ChIMES) was used in 7.9% of the studies. Of the 8155 pediatric patients evaluated, 47.7% had both hematological malignancies and malignant solid tumors, while 46% had solely hematological malignancies. Despite the prevalence of the WHO scale, it lacks pediatric‐specific criteria. Future OM research should incorporate validated tools like ChIMES for improved pediatric assessment.