Technological advances afford teacher educators, designers, and researchers the opportunity to use videos as an instructional tool to help parents, caregivers, teachers, and other adults support young children's mathematical development. We created five Magic Math Minute videos to highlight examples of young children's mathematical thinking and to show how adults can engage children in mathematics conversations. We intended for these videos to inform adults about the ways children explore mathematics and to foster productive adult-child interactions around mathematics. This article documents how we designed five distinct but related formats of a Magic Math Minute video. It describes the video content, design constraints, three online studies evaluating the videos, and how the results of these studies informed revisions to our design.