The U.S. Census Bureau’s Demographic Analysis shows the population age 0 to 4 experienced a net undercount rate of 4.6 percent in the 2010 Decennial Census. This is more than twice as high as any other age group. Despite the fact that the relatively high net undercount of young children was uncovered more than fifty years ago, this problem has received little systematic attention from demographers. To help fill that gap in the literature, this study examines the accuracy of the count of children in the 2010 Decennial Census. The initial focus on all children shifts to a focus on young children (age 0 to 4) where net undercount rates are the highest. Discussion highlights some of the potential explanations for the findings.