Every new stage of my little girl's life sneaks up and surprises me. We were discussing germs just the other day, and she was soaking it all up hungrily! Clearly she's old enough to begin to learn more concrete things about her amazing growing body. I realized I might need some more concrete information than my spotty knowledge, and the hunt for good books and puzzles about the human body began.
There are actually tons of great resources out there, but a lot of them are geared for older kids, not preschoolers. DK Books is always a great place to start for learning books, and I've included one of theirs here. Plus, I found a couple of other books with illustrations that look really appealing. I've heard great reviews of the discontinued Your Human Body book too, which you can find used on Amazon. Beleduc's puzzle is a great beginners choice, and the Janod puzzle will grow with your kids - just highlight more details as they get older. I have a feeling I'll be learning right alongside my kiddo.
(Images as linked)