Not enough here to be useful.
It's one of those picture books that tries to talk about bodies and sex, and just doesn't talk about the hard parts. Also, I'm fairly sure that they don't actually mean that your "head, arms, hands, legs, and feet" are used "every time you hug your mom, ride a bicycle, or eat a snack." I usually don't use my feet when I eat a snack. I imagine there are some people that do, like people don't have hands. At any rate, it describes private parts as "the parts that nobody else but you sees," which is not accurate, because your parents see those when you're younger, like if you're a preschooler, which is the age this is aimed at. Your parents are going to bathe you. Your doctor's going to look at you. But it doesn't mention anything about bad touching, about not letting anybody else touch you there, or look at you there, which would be helpful.
It's not inclusive of transgender people, but that's fairly typical for books aimed at children this young, especially ones which were written decades ago (2005 in this case) so it's dated because it doesn't explain or leave space for that. It basically says, if you're a girl, you have a vagina. It doesn't use the word "vulva", but it uses the word "vagina" correctly-- it says the vagina is covered by labia. It mentions the urethra, and talks about boys and their penises and scrotums. It says that it's okay if you touch yourself, but you should do it in private. It shows illustrations of boys growing into men, and girls growing into women. They're multicultural and have no armpit hair, and the man doesn't seem to have any pubic hair, either. Here's as close as it gets to discussing sex: "When a man and a woman love each other and decide that they want to have a baby, a man's sperm joins with a woman's egg. From the egg and sperm, a baby will grow." There's a lot missing from that sentence, and that's the hard part to talk about. The easy part to talk about is, 'These two things come together-- Tada!'
It mentions the umbilical cord, which is nice. It talks about babies being born vaginally but doesn't leave room for cesarean sections. I'm getting tired of that in books. It's nice that it mentions the vagina is stretchy.
It's not really helpful. It's just not useful to anybody having a complex discussion. I mean, yeah, preschoolers are going to understand it, but there's important things you need to be discussing with preschoolers in addition to this-- People not touching them inappropriately and similar ideas, because you need to really talk about that before it might happen. You want to head that off ahead of time. At any rate, it's not bad, but it's not great. There's not enough to it. It goes into a little bit more detail than the book "Who Has What?" by Robie H. Harris, but not too much. And that's not a very high bar.
Also, the illustrations are rather cartoony, which is annoying when talking about something this complex and important. They're not realistic enough for me.