What are leveled readers?

Before we dive into 《小羊上山》, I just wanted to take a moment to explain what leveled readers are.

Leveled readers are books that have been specifically designed to help children improve their reading skills at different levels of difficulty. They are typically categorized according to a reading level system, which can be based on a variety of factors such as vocabulary, sentence structure, and overall complexity. Leveled readers can be used to provide targeted reading practice and support for children at different stages of their reading development.