Fairy tale books can help children improve their imagination and broaden their horizons. For example, grimm's fairy tales and Aesop's fables.
Historical biography books can enrich children's knowledge reserves. For example, five thousand years.
Popular science books can enhance children's imagination and creativity, such as "100,000 Why".
Children's literature books can improve children's emotional intelligence. Such books are most popular with children because they are closer to their lives. What I recommend most is Hu Xiaoxiao's Diary. The story is particularly interesting and instructive, and it can also help children shape their character. If you still don't know what to buy for your child, I suggest using this set as a primer for your child.