Richard Little 
I Know Flat and Solid Shapes [PDF ebook] 

It is not just important for young learners to master familiar shapes like triangles, circles, and squares. Recognizing and identifying two-dimensional ("flat") or three-dimensional ("solid") shapes is a geometry standard of Common Core math. This helpful book, written to be accessible for our youngest learners, allows readers to compare 2-D shapes with their 3-D counterparts, such as a circle and sphere. Photographs clearly illustrate the qualities that define each. Concluding questions help readers review geometric terms.