Purpose: The purpose of this study was to report the prevalence of early childhood caries (ECC) and severe early childhood caries (S-ECC) in the United States and to examine trends from 2013 to 2018 in children under six years of age. Methods: Data were obtained from National Health and Nutrition Examination Survey (NHANES). Data from three consecutive cycles (2013 to 2014, 2015 to 2016, and 2017 to 2018) were analyzed. A total of 3,157 children younger than six years of age were included in the analysis. The proportion of children with ECC who developed S-ECC was calculated to assess the severity of the disease burden. Multivariable logistic models were used to determine the significance of both linear and quadratic trends. Subgroup analyses were done to test trends in different population groups. Results: The overall prevalence of ECC from 2013 to 2018 was 18.6 percent; the overall prevalence of S-ECC during this interval was 10.6 percent. The prevalence of ECC decreased from 2013 to 2014 (19.6 percent) to 2015 to 2016 (17.4 percent) but increased from 2017 to 2018 (to 18.7 percent). By contrast, the prevalence of S-ECC increased substantially from 2013 to 2014 (9.8 percent) through 2017 to 2018 (11.9 percent). The proportion of children with S-ECC among those with ECC increased from 2013 (49.9 percent) to 2018 (63.4 percent; linear P=0.048) with a significant linear increase among five-year- old (P=0.013), males (P=0.037) and children in families with income 100 percent of the Federal Poverty Guideline (P=0.003). Conclusion: A greater proportion of children with early childhood caries developed from 2017 to 2018 versus 2013 to 2014.