Child Poverty Reduction Act of 2021 This bill requires the Department of Health and Human Services (HHS) and the Census Bureau to take certain actions with respect to poverty measures and data related to child poverty. It also requires the National Academy of Sciences to report annually on child poverty and study other issues, such as policies to reduce intergenerational poverty. Specifically, HHS must enter into an agreement with the Census Bureau to annually report an anchored supplemental poverty measure for individuals under the age of 18 and must otherwise collaborate with the bureau to, for example, correct income data to account for underreporting. Currently, the Census Bureau uses the official poverty measure (based on cash resources) and the supplemental poverty measure (based on both cash and certain noncash resources, such as nutrition assistance program benefits) to measure poverty. Anchoring the supplemental poverty measure fixes the poverty threshold at a given point in time and then adjusts it for inflation. HHS must publish resources on its website related to child poverty, and the Census Bureau must release certain economic and survey data at the same time it releases a specific report related to income, poverty, and health insurance coverage in the United States.