This is geared for 7-9 year olds to explain things in an age appropriate discussion. It's a companion volume for the book "It's Perfectly Normal," which is geared for 10-15 year olds. I first skimmed that book to review for my twins, who will be turning 9 soon. However, they are definitely not mature enough yet, so I borrowed this book on Libby to review instead. It is much more appropriate for their maturity level.
For the most part, it is straightforward and gives much information, but not too much so as to overwhelm them. I have two comments, though.
The first is that I read an older version, which equated sex and gender and did not mention transgender or nonbinary. I placed a hold for the updated version, which is only available through my library in print, but it hasn't come in yet. I hope this inaccuracy is corrected in the later edition, and will update my review when I can confirm that it has been.
The second comment is regarding the chapter on menstruation specifically. While it is accurate and relatively thorough regarding the general concept, it does not go into great detail. For example, it doesn't mention cramps. Girls can enter puberty as early as 8-9 years old, which is my main motivation for researching this now. "It's Perfectly Normal" contains much more information about what to expect each month and how to deal with it. So, my plan, I think, will be to purchase both books, and start with reading "It's so Amazing" cover to cover with both my son and daughter. Then, as they enter puberty and things start to happen, I will use the other book as a reference, reading the relevant chapters with each of them as the need arises. So my daughter will know what to expect when she gets her first period, and we can delve into the specifics at that time.