Fatigue resulting from unpredictable or extended working conditions is a factor that negatively impacts the performance of police officers. In this study, we considered how investigative interviewing of children is influenced by interviewer working conditions. We examined two working conditions concerning when interviews were conducted: (a) during early duty shift and (b) an hour before the end of an interviewer’s duty shift and after the end of a shift. We analysed 102 police interviews with children and identified clues that interviews which commenced during early duty shift had more appropriate approaches than interviews in the other condition. Inappropriate approaches were not significantly affected by interviewer working conditions. These outcomes suggest considering new knowledge specific to the behaviour of interviewers according to working conditions and provide promising foundations for further research.