In China, hundreds of millions of migrant workers have moved to cities or coastal regions for more or better-paid jobs and have left their children behind at their rural homes. Separated by thousands of kilometers, these "left-behind" children and their migrant parents use mobile phones as their primary-and often only-method of maintaining family connections. To better understand the use of technology in this long-distance communication, we conducted a multi-phased study using interviews and surveys in three different Chinese rural areas. In this paper, we report our findings on how these children communicate with their migrant parents and what information they exchange. We also discuss design implications derived from these findings that may improve communication between left-behind children and their parents.