Introduction Most pediatric cancer patients in developing countries present at an advanced stage due to delayed diagnosis, being an important barrier to effective care. The objective of this study was to evaluate the associated factor of patient delay and explore significant parental practice‐associated risk factor to patient delay. Methods This was a sequential mixed methodology, utilizing data from the Indonesian Pediatric Cancer Registry for clinical variables and completed interviews with parents using structured questionnaires to obtain their sociodemographic data. A binary logistic regression analysis model was fitted to identify factors associated with patient delay. Additional semi‐structured interviews related to parental practice of using complementary and alternative medicine (CAM) were administered to 30 parents. Thematic framework analysis was performed on qualitative data to explore determinant factors of parental practice of using CAM. Results We interviewed 356 parents with children with cancer. The median patient delay was 14 days (interquartile range [IQR]: 6–46.5 days). The most extended delay was in patients with malignant bone tumors (median 66, IQR: 14–126). In multivariable logistic regression analysis, solid cancer (odds ratio [OR] = 5.22, 95% confidence interval [CI]: 2.79–9.77, p < .001) and use of CAM (OR = 1.86, 95% CI: 1.13–3.08, p = .015) were associated with patient delay. Qualitative interviews highlighted key issues relative to determinant parental factors using CAM, including vague initial childhood cancer symptoms, parental health‐seeking behavior, CAM availability and accessibility, also barriers of healthcare facilities. Conclusion Type of cancer and use of CAM are essential factors that cause patient delay. It should be addressed in the future childhood cancer awareness and childhood cancer diagnosis pathway.