We have started on our unit one of the Human Body. We have taken a few days on it as it is a lot of information.
I have made these handy notebook pages to help Daniel understand better the subject.
Also there is a subscription of "How Your Body Works" we have and with the subscription comes a handy Skeletal Body part that you can build with your kids as well as other freebies you can enjoy. I love this one since we learn best when we build and touch stuff.
Along with this you may enjoy taking a tour through "Kids Discover" magazine page and download a few freebies and lesson plans as well as a Apps you will love your kids to have.