Smartphone applications are widely used for self-help interventions in adult cancer survivors. However, applications for parents of pediatric cancer patients are limited. We developed an applications to assist parents of children with acute lymphoblastic leukemia. The aim of this study is to evaluate the app's usability and effectiveness in a preliminary way. A stepwise approach and mixed methods were used. The application was initially tested by healthcare providers, and their comments and suggestions were used to develop an updated version. This version was tested by parents of children with acute lymphoblastic leukemia. Comments and nonverbal expressions of parents were recorded during a 2-week pilot test. The qualitative study was followed by a quantitative study using audit log data from the administration portal to understand how parents use the application. Six healthcare providers and 15 parents participated. Parents gained a greater knowledge of leukemia, confidence in caregiving, social support, and information on how to reduce stress. Over usability was rated as stable, useful, simple, and self-explanatory. No software failure occurred. Applications have the potential to support caregivers of pediatric cancer patients. We plan to address limitations and perform an empirical interventional study to examine its clinical effectiveness.