Project Summary Early childhood development (ECD) plays a crucial role in shaping an individual’s lifetime health, development, and social wellbeing. Ensuring all girls’ and boys’ access to quality ECD is one of the components of the Sustainable Development Goals (SDGs). Early adversities are found to be linked with increased risk of poor early development and deficit in schooling year, income loss, and mental and physical health issues in later life. Quantifying the prevalence of children being exposed to the risks of poor development in their early life is important for understanding the challenges of fulfilling young children’s developmental potential, identifying areas for policy interventions, and evaluating the progress of eliminating the risks. The 2007 and 2017 Lancet ECD Series spearheaded the efforts of generating the estimates (for 2004 and 2010 respectively) of global-, regional-, and country-level prevalence of young children exposed to stunting or extreme poverty in low- and middle-income countries (LMICs). These estimates have been frequently cited by policy documents and academic papers. The proposed study will update the estimates of prevalence in LMICs with two specific aims. (1) Using the most updated data and a new definition of extreme poverty, we will generate composite measures of young children’s exposure to stunting or extreme poverty in 135 LMICs over four time periods (2000-2005, 2006- 2010, 2011-2015, and 2016-thereafter). The evidence will allow us to assess the progress in reducing young children’s exposure to the two risks in the past 20 years, especially during the era of SDGs. (2) To better understand the challenges of reducing the risks of poor development in LMICs, we will add two more risks (low maternal schooling and maltreatment in early life) to the composite measure for a subgroup of LMICs that have data available in their household surveys. We will also assess the levels and trends of socio-demographic disparities in risk exposure by age, sex, and residential area at the country- and aggregate-level. Assessing disparities will allow us to identify the most vulnerable young children in these countries. To examine the robustness of the findings derived from these two aims, we will also use the moderate poverty measure, defined by the World Bank, in our estimation.