A case of style over substance.
There are a lot of things I like about this book, but it's vague, and some of what it says can be misleading. It's written mostly in a conversational style, with a child of unknown age and indeterminate gender who asks his or her grandmother, "Tell me about sex, Grandma." And the grandmother says, "Well, whattaya want to know?" The kid says, "What's so bad about it?" "Who says sex is bad?" And the kid makes a good point, explaining that nobody lets them see it or talk about it, so it must be bad. It can't just be a "grown-up thing", like the grandmother suggests, because coffee is a grown-up thing, and the kid can see and talk about that.
The grandmother then defines sex as, "A thing with bodies. Moving so it feels good. By yourself or with someone." Which really makes it sound like giving somebody a massage is sex. I think that the depicted child already has some kind of knowledge about sex, and is asking more for clarification than information. "How do I know how to move?" says the kid. "The feelings tell you." It would be nice if it were that simple, and nothing sexual was ever awkward or uncomfortable, or even painful. This ignores the collected wisdom of the ages, only recently available to the average (industrialized) adolescent through the magic of the internet (I'm talking about things like the Kama Sutra and "Go Ask Alice" and "Scarleteen"). But this book never uses the word "penis" or "vagina", both a point in its favor, as it makes it open to interpretation of all sorts of various possible sex acts between people of any gender, and a mark against it, because it doesn't discuss what the vast majority of people think "sex" means in an anatomical fashion. And it doesn't mention that in the overwhelming majority of people, at least one of those organs is involved in "sex". On the other hand, though, "sex" doesn't always involve bodies moving. It can be entirely mental, or verbal. It can be visual. If you're going to be vague about it, why not just go all the way?
The kid asks if sex always makes a baby, and the grandmother says no. Without any explanation of how to lower the chances thereof, or what in fact happens if sex does make a baby. The kid mentions masturbation (again, without using the word "masturbate") and the grandmother says it's okay but it should be private.
One great thing about this book is it answers questions you might not expect your children to ask, or the children might not know to ask. "Why don't adults want kids to know about sex?" "Our job is to protect you." "From sex?" "Growing up too fast. And from people who don't follow the rules." And it's important that kids know what those rules are, in order to protect themselves. We parents aren't able to watch them every single moment of every day. We can only do so much, and it's our responsibility to instill self-defense in our children. The grandmother explains the rules as, "No sex with anyone unless they say they want to, and no sex, ever, with kids. It's harmful. It's against the law. And anyone who tells you different is lying. Once those rules are respected, a person's sexuality is no one else's business." Which is a really great message, said in a well-crafted manner. This book is very sex-positive and inclusive (mostly due to its vagueness). There are definitely important things that it successfully gets across, and places where it's necessarily explicit in its message (like the previous quote). But again, without a clear definition of "sex", it's just doing what the title says, and talking "about" sex. It's begging the question, assuming the reader already knows what it is.
It talks about body language a bit, and feeling worried about things and trusting your body when you feel nervous, and how sometimes other people make decisions for you against your will (like your parents telling you it's time to go to bed). It says to be careful because there are images out there that will basically mentally scar you for life, so you need to be careful to pick someone who you trust to ask about this kind of thing.
This book barely skims the surface of the topic, but it skims it well. But it's not enough to answer the larger, underlying question of what sex actually is. It's incomplete, and it reads more like a meditation on the process of talking to children about sex than an actual instructive book. I would love to see a thorough, detailed book about sex written in this style. It drew me in through its conversational tone, but left me wanting something more substantial. The artwork is great, as well.