Each of the board books in this quartet feature the same three young children who demonstrate simple math concepts in real-life scenarios through the four seasons. In the spring, Mei plants a sunflower seed and then uses her body (toe, knees, waist, shoulders) to measure the growth of the sunflower in Up to My Knees! In Circle! Sphere!, Manny joins Olivia and Mei in the summer to introduce elementary geometric shapes as they blow bubbles in the backyard. What Will Fit? has Olivia exploring spatial reasoning by considering how different fruits and vegetables do (or don't) fill her basket at an autumn farmers' market. And when Mei and Olivia come inside on a cold winter day in The Last Marshmallow, they warm up with hot cocoa and figure out how to divide three marshmallows into equal shares. Olivia is Black, Mei is Asian and brown-skinned Manny is likely Latino; all are engaged, curious children exploring their everyday world through math. Each book concludes with a double-page spread for adults that includes more about the concept introduced in each volume and a practical "Try This!" section with tips on ways to extend the math exploration with children. (Ages 2-4)