This is the packet I use for our 4th graders (boys and girls together) when we talk about Health and Hygiene. I also use the book, "Hygiene...you stink!" by Julia Cook as well as the video, "C.A.T.C.H. onto Good Hygiene.
This first lesson is usually 30-45 minutes.
The second lesson (not in this packet) we focus on "Puberty." (boys and girls separate).