While AI is a great tool for creating artworks for your book, it has some limitations:
The AI illustrator can't count, which means that if you want 5 cats and 1 mouse, you might get 5 mice and 3 cats.
AI can't generate consistent characters even if you use the same prompt. You might get characters that look similar, but you'll never get the same character.
AI is not very good at interpreting complex, nuanced language. While it does help to write specific and detailed prompts, writing them in a very creative and nuanced manner will confuse the AI.
AI has a limited understanding of image context, which can result in scenes looking unrealistic.
AI can't draw complex 3D scenes. Simple 3D scenes work, though.
AI can't spell so if you have signs in your images, they will most likely spell rubbish.