Lisa Trumbauer has written early-learner books for Scholastic's Jump Start series and published numerous other activity books, picture books, and novels for middle-school readers, including the New York Times bestseller A Practical Guide to Dragons.
The Rookie Read-About Science series is great! The series does double duty. It's easy for young readers to read by themselves or practice reading aloud to a parent. Also, the concepts are easily explained easily for them to understand and learn.
This book introduces friction using many different ways such as animals, matter, and geographical features. These are all things that children have been exposed to before so they will be able to understand the concept easier.