Building Blocks of STEM Act This bill modifies National Science Foundation (NSF) grant programs that support STEM (science, technology, engineering, and mathematics, including computer science) education. The bill instructs the NSF, when awarding grants under the Discovery Research PreK-12 program, to improve the focus of research and development on early childhood education. The bill specifies that NSF grants to increase the participation of underrepresented populations in STEM fields may be used for research into various subjects regarding female students in prekindergarten through elementary school, including the role of teachers and caregivers in encouraging or discouraging participation by such students in STEM activities, and the types of STEM activities that encourage greater participation by such students. The bill specifies that NSF grants to research computer science education and computational thinking may be used to support development and implementation of various tools and models for teaching and learning, including developing and offering gender-inclusive computer science enrichment programs, and acquainting female students in prekindergarten through elementary school with careers in computer science.