Background: In recent years, children's hospitals have increasingly implemented postoperative pain management protocols to reduce postoperative pain and improve patient satisfaction. The effectiveness and long-term sustainability of such protocols have rarely been studied. Therefore, we conducted a prospective intervention study to assess the impact of regular training and improvement of clinical processes on the quality of postoperative pain management. Methods: We conducted an initial assessment of the status quo of postoperative pain management (Audit 1) followed by repeated training and improvement of clinical processes (analgesic pocket card, parents' brochure, modification of the patient chart, bimonthly advanced trainings sessions) and a follow-up review after 3 years (Audit 2). We used a data entry form, a patient survey, and an anonymous questionnaire for the nursing staff as measurement tools. Results: Our analysis included a total of 93 and 85 patients in the initial and final audits. The return rates of the nursing staff questionnaire were 83% (Audit 1) and 77% (Audit 2). The training and process improvements resulted in significant improvement in the administration of analgesics for pain requiring treatment, the control of pain measurement after the administration of analgesics and the use of non-pharmacological pain therapies. The patients reported faster administration of analgesics for acute pain and improved pain relief following the intervention. Conclusions: Repeated training and improvement of clinical processes can significantly improve the long-term quality of postoperative pain management in children with a tolerable amount of effort on the part of health care professionals and institutions.