Most picture books are enjoyable for kids, 0 and up. Especially handsome ones. However, kids can begin to follow the Bax narrative at about 4 years old or so, and can probably be read on their own by ages 6-7. (Each book also has entertaining side-rails which help make it more fun for adults.) The curriculum itself is designed to scale with your child. You can discuss a WORD itself, the IDEA in which the word sits, or how that idea RELATES to a child's life with varying levels of complexity. Regardless, the lessons are fun, audibly tasty, and in some cases nicely driven by visuals.