We are developing an affordable and comfortable new mobile sensing device (called LittleBeats™) that children between age 3 to 24 months will wear in the home. LittleBeats™ is equipped with sensors to measure motion and heart rate, as well as a microphone to record audio. Designed with a small and sleek shape, the device easily fits inside of a specially designed shirt pocket. It is attached by placing three hypoallergenic gel stickers on your child’s skin. It is safe and works with children as young as 1 month old. Our goral is to understand the relation between activity and surrounding context of children along with with interaction with parents and their mental development.