i think ur in the wrong place for this but ok lol
Consider age range first, some things are just too soon to be showing kids.
that said, it can be done tastefully so long as the illustrations are done similarly to medical diagrams. Like, dont show any skin, especially in private areas. but the nervous system, muscles, bones, organs. fair game.
maybe consult medical books and simplify the terms
I'm in the medical field also about body part I was just going to do circulation and nervous system at first the thing is I struggle with is if the book can be understood by children who are 7 years old
So il writing à children book about human body than environnement than ofc space but as iam writing I find myslf thinking maybe they won't understand without drawing or it would have been better if I could make it like manhwa or manga idk what to do do they understand thing like branches and alveoli ? If I don't showit to them any idea