This working paper estimates participation in early childhood education (ECE) programs by child's age, program setting, family income level, and child's household language. To produce the best possible estimates of participation, the authors combined information from multiple data sets. In 2010, approximately 6.6 million between the ages of 2 and 5 attended a center-based preschool program. By age this breaks down as: 3 million at age 4, 2.2 million at age 3, and 1.4 million at age 2. Comparable numbers of low-income children are 1 million at age 4, nearly 700,000 at age 3, and more than 400,000 at age 2 for a total of roughly 2.1 million. In 2005, the bottom income quintile corresponded closely to children in poverty. However, the poverty rate for children under five had climbed to 25% by 2010 due to the recession. Therefore, to be more precise for 2010 we estimated the numbers of children in poverty in various ECE arrangements by multiplying numbers for the lowest quintile by 1.25. We estimate the number of children in poverty attending centers in 2010 as roughly 660,000 at age 4, 470,000 at age 3, and 260,000 at age 2 for a total of about 1.4 million. As the economy improves, these numbers should fall back toward those in our tables as the numbers of children in poverty fall back toward pre-recession levels. (Contains 10 tables.)