Children living with parental mental illness are hidden populations. This study aims to explore the perspectives of mental health professionals regarding these children, with a focus on their work experiences, potential barriers to intervention, and suggestions for service provision. Twenty-seven participants in Taiwan took part in semi-structured interviews, including fourteen psychiatric social workers, ten community mental health social workers, and three community nurses. The data were analyzed using thematic analysis. Three key themes emerged from the participants’ experiences: children excluded from meetings, family struggles in silence, attempts to find solutions. These themes highlighted that children of parents with mental illness were often overlooked by services due to parental fears of being assessed as incapable and the social stigma related to mental illness. Building a trusting relationship with parents was essential, achieved through professional skills such as genuine listening, showing respect for the parents, and reassuring them that the goal of service involvement was to strengthen family functioning. A family-centered approach was emphasized, involving children in family meetings to listen to their voices and understand their lived experiences. Recommendations for services to support the needs of children living with parental mental illness are outlined.