A socially assistive robot (SAR) can support children in developmental and well-being aspects. Children's tendency to anthropomorphize and pretend play contributes to their ability to engage with robots and establish relationships. The robot's visual aesthetics influences users' initial judgments and is essential for creating first impressions, trust, and desirability. SAR's visual appearance may lead the child to desired assumptions about its capabilities. Beyond aesthetics per se, designers must address the robots' visual qualities necessary to affect users' perceptions and expectations. This paper proposes and demonstrates a methodology for evaluating children's perception of visual qualities in SARs, aiming to pave the way for new design tools to support robotic designers and developers. Design tools can improve the SAR design process by forming means for designers and roboticists to consider and create a user experience for specific contexts, tasks, or use-case scenarios relevant to particular SARs. By this, to form the design of more use-oriented, acceptable, trustworthy, and desirable robots.