Objective: Through interviews, this study aimed to clarify the parenting concerns of cancer-affected mothers with children of all ages, from infancy to adolescence. The study also examines how support should be provided to mothers and families according to the children's age. Methods: Semi-structured interviews were conducted with 12 mothers with cancer. We asked them the following questions: 1) How has the cancer diagnosis affected your roles and responsibilities as a parent? 2) How have your children influenced your treatment choices and decision-making? 3) What distress did you feel when deciding to tell/not tell your children about your cancer diagnosis? 4) What are your parenting concerns, and what support and resources do you need to address them? The data were transcribed verbatim and classified into categories, subcategories, and codes. Results: The parenting concerns were classified into eight broad categories. The features and tendencies of the expressed concerns were characterized differently depending on the children's developmental stage. Conclusions: The parenting concerns of patients with cancer differed according to their children's age. Some concerns about social support were adjudged to be trends unique to Japan, as previous research in Europe or North America did not reveal such findings. Furthermore, the mothers desired support from medical personnel for their children and families. According to this study, it will be necessary to provide age-appropriate parenting support to children in the future; this support must include the patients and their families.