This study explores the factors associated with the quantity and quality of children’s testimony in police interviews, focusing on the characteristics of the crime, child victims, interviewers, and interview surroundings. We collected 137 cases of children interviewed as victims of a crime by administering a questionnaire to police officers in charge of the cases across Japan. Categorical principal component analysis, applied to the officers’impressions of the child’s accounts, yielded two aspects of the testimony: the quantity/quality of testimony, and the level of usability in the investigation. Regression analyses with variable selection revealed variables associated with these two aspects. The quantity/quality of testimony was associated with the characteristics of the crime, and the interviewer’s investigation experience, empathy, and history of participation in training, while information usability was related to the children’s characteristics, and the interviewer’s opportunities to talk with children other than their own, outside of work. The timing of the interview was also suggested to be involved in the two aspects of the children’s testimony. Limitations of this study are discussed for future studies.