Over the years, Yoo has studied and published picture books for different topics. Her first children book was Super Turtle which was followed by Super Rabbit which have been loved by children and grownup readers alike. Super Turtle tells the story of what happens to the turtle after winning the race against the rabbit, and the book prompts young readers to think about what it means to be themselves. Super Rabbit tells the story of what happens to the rabbit after losing the race, and it teaches young readers about overcoming their failures. After meeting and talking with children, the writer has been asked to write their stories in picture books. Yoo has been writing about the problems and conflicts children face in school and the ways to overcome them. Her series of Glove Elementary School include Good Job, Twin Mittens!, Overcome Your Fears, Plastic Glove!, Stop Being Greedy, Lace Glove!, Lying Makes Rubber Glove Go Poot-Poot!, and Don't Be Jealous, Baseball Mitt. Her other picture books are A Magnificent Dog's Mansion and Band Bremen.