Acute lymphoblastic leukaemia (ALL) is the most common childhood malignancy. Caring for children with ALL is an uncommon experience for parents without medical training. They urgently need professional assistance when their children are recovering at home. This paper documents the process of developing an Android application (app) "Care Assistant" for family caregivers of children with ALL. Key informant interviews and focus group studies were used before programming the app. The key informants and focus group members included: caregivers of children with ALL, cancer care physicians and nurses, and software engineers. We found several major challenges faced by caregivers: limited access to evidence-based clinic information, lack of financial and social assistance, deficient communications with doctors or nurses, lack of disease-related knowledge, and inconvenience of tracking treatments and testing results. This feedback was used to develop "Care Assistant". This app has eight modules: personal information, treatment tracking, family care, financial and social assistance, knowledge centre, self-assessment questionnaires, interactive platform, and reminders. We have also developed a web-based administration portal to manage the app. The usability and effectiveness of "Care Assistant" will be evaluated in future studies.