In this paper, we present the design evolution of two social media (SM) tools: Scientific INQuiry (SINQ), which transformed into ScienceKit. We detail our motivations for using SM tools in science learning and the design decisions we made over a 2-year, design-based research project. Our designs grew from our experiences using SM tools in the field and co-designing these systems with children. Our longitudinal case study and design narrative contribute to our understanding of the design and use of SM tools to support children's scientific inquiry. Specifically, we detail (1) the affordances and constraints we gleaned from the design evolution of SINQ to ScienceKit, (2) the potential of SM to guide learning behaviors, and (3) the role of SM for children and the community of adults and peers who support them.