Introduction: The KLIK Patient Reported Outcome Measures (PROM) portal (www.hetklikt.nu) has been implemented since 2011 in clinical practice in over 20 Dutch hospitals. Patients and/or parents complete PROMs before the outpatient consultation and answers are subsequently discussed by clinicians during consultation. This study aims to provide insight into patients’ and parents’ perspective on the use of the KLIK PROM portal in order to optimize its implementation in pediatric clinical practice. Methods: Patients (12–19 years) and parents (of children 0–19 years) from the Emma Children’s Hospital were invited to participate. A mixed-method design was used; (1) Focus groups were held and analyzed using thematic analysis in psychology, (2) a questionnaire was sent out and analyzed using descriptive statistics. Results: (1) Eight patients and 17 parents participated. Patients mentioned that KLIK has an attractive layout. However, PROMs were sometimes considered irrelevant and repetitive. Parents valued that KLIK provides insight into their child’s functioning, but they were not satisfied with the extent to which PROMs were discussed by clinicians. (2) 31 patients and 130 parents completed the questionnaire. Overall, patients and parents reported a satisfaction score of 7.9/10 and 7.3/10, respectively. 81% of patients and 74% of parents indicated that KLIK is easy to use. Conclusion: Patients and parents are generally satisfied with KLIK, however, points of improvement were mentioned. These are currently being addressed by e.g., upgrading the KLIK website, implementing PROMIS item banks in KLIK to reduce irrelevancy and repetitiveness of PROMs, and implementation strategies to improve the discussion-rate. In this way, implementation of the KLIK PROM portal can be further optimized, with the ultimate goal to improve quality of care.