Haptic feedback displays are an emerging technology that have the potential to enhance how children and their parents interact with and learn about science concepts. Yet, we know little about how to design haptic feedback applications for science learning or how children and their parents make use of these interactive features. This paper presents the design and evaluation of TCircuit, an application for a variable friction touch-screen display (i.e., Tanvas Tablet) that enables parent-child dyads to feel electric current flowing through a circuit diagram by touching the display. We describe results from a formative design study with 10 parent-child dyads that reveal which texture patterns and mappings are most appropriate for representing the concept of electrical current through haptic feedback. We also report results of a comparative study with 40 parent-child dyads in a museum setting. Our analysis shows that dyads in the haptic condition performed slightly better when predicting their answers to learning tasks. However, we found that haptic feedback introduced new complexities for how dyads perceived and discussed the exhibit content. We discuss the potential for haptic feedback displays to support science learning, particularly in collaborative settings, and design considerations for future systems.