This study employed a single factor experiment to investigate how different voices from a social robot affect the learning outcomes and motivation of 46 children. The learning motivation for the participants was measured using the ARCS questionnaire, which tested for four subcategories: attention, relevance, confidence, and satisfaction. The results showed that a social robot's voice significantly affected children's motivation to learn, with the children preferring a social robot with a child's voice. However, the voice of a social robot exhibited no significant impact on their learning outcomes. The findings of this experiment are of value to those involved in designing children's learning material that uses social robots and to those who work on interaction design with children.