Beyond just reading, these books can spark interest in the English language and culture. They also provide a great way to practice English in a contextual learning environment. In short, reading children's and young adult books in English is a fantastic way to improve your English while having fun.
Reading fiction is one of the best methods for Extensive Reading, which helps you absorb language naturally over time. It's a method that strengthens your reading comprehension and helps you build vocabulary in a meaningful context, far more effectively than just memorizing word lists.