This is a resource I wish I had when I was writing my first book. Instead I've received it a year and a half later as a Goodreads giveaway. And it really is a good overview by an author who has several books published.
That's all it is, though, an overview. The chapters are extremely short, lacking a certain depth I had expected from a book about mastery. Despite some vocabulary, it feels like it could very well be How to Master the Art of Writing Children's Books, Kids Edition. This isn't a bad thing, though. A book about writing books for kids that's accessible to kids would be fantastic.
Although one thing that did get some depth was poetry. You can tell this author loves poetry (which she attributes to Dr. Seuss in her acknowledgments, which isn't surprising). There's discussion of rhyme schemes and meter that I think would benefit authors of other Goodreads giveaways I've received. But she's obviously much more interested in this than other aspects of storytelling.
Another quibble I had was a quick note in the section about graphic novels. There's a mention about the different age groups graphic novels could be written for, with the last mention of "and even adults." My first instinct was that she included this because it was a surprise to her. But it could be that she expects readers to be surprised by this even though graphic novels for adults have existed for decades now.