Art is assumed to possess therapeutic benefits of healing for children, as part of patient-focused design in health care. Since the psychological and physiological well-being of children in health care settings is extremely important in contributing to the healing process, it is vitally important to identify what type of art supports stress reduction. Based on adult studies, nature art was anticipated to be the most preferred and to have stress-reducing effects on pediatric patients. Nature art refers to art images dominated by natural vegetation, flowers or water. The objective of this study was to investigate what type of art image children prefer, and what type of art image has potentially stress-reducing effects on children in hospitals. This study used a three-phase, multi-method approach with children aged 5-17 years: a focus group study (129 participants), a randomized study (48 participants), and a quasi-experimental study design (48 participants). Findings were evaluated from three phases.