Early childhood is a critical time for the development of social skills. However, some children struggle to develop social competence due to a variety of factors. Although supporting social development is an instructional goal for many early childhood educators it can be difficult to measure these skills objectively in order to inform instruction. This manuscript provides results from a two-phase validation of a new, unobtrusive, wearable sensor technology designed to objectively measure social engagement among young children in educational settings. As a first step to validation we focus on the constructs of proximity and frontal orientation, key indicators of early social engagement. We validate these modalities by comparing sensor data to video coded data for social engagement between child-child and teacher-child dyads. Results provide initial evidence that the wearable sensor technology can accurately measure social engagement for children and their teachers in early childhood settings. Limitations as well as future adjustments and validations to the sensor technology are discussed. We also discuss practical applications and future research directions. (author abstract)