Research exploring nurses' experiences working with families in paediatric intensive care unit (PICU) is limited. No studies have been undertaken in a mixed adult-paediatric ICU.To explore nurses' perceptions of working with families of critically ill children in a mixed adult-paediatric intensive care unit (ICU).Descriptive qualitative design.Five PICU nurses participated in semi-structured interviews. Data were analysed using thematic analysis. Trustworthiness was enhanced using an audit trail, member checks and peer review of all data.Three main themes and one overarching theme emerged. Role confusion and delineation examined the roles which nurses ascribed to themselves and the families; and demonstrated the conflict which could arise if roles were challenged. Information sharing demonstrated the positive and negative ways in which nurses utilized information with families in their daily practice. The contextual environment of the PICU scrutinized the physical, cultural and institutional factors which impacted on the nurses' ability to work with families in the PICU. Finally, the overarching theme Competing values explores the interplay between the nurses' personal values and those of the PICU and the institution.Working with families in a mixed adult-paediatric ICU is influenced by multiple personal and institutional factors. The value placed on families and on the time nurses spent with them often competed for priority with nurses' other values and the wider culture of the PICU. The potential for role confusion, the management of information and the physical environment of the PICU further contributed to variability in nurses' working with families.The results highlighted a need for education for both nurses and medical staff who work with families of critically ill children. Additionally, the need for each PICU to have a written policy on family presence and participation is crucial to guide practice and maintain continuity of care.