I enjoyed teaching Light and Shadow in elementary school. Here are some of the things from my notes:

Lesson #1
1. What is a shadow? The shady area made by something that has light shining on it.
2. Students hold their pencils vertically on their desks, and I ask, "which side of the pencil will the shadow be on?" Then I turn on the light - probably a spotlight or a lamp without a shade.
3. The kids had a light bulb on a stand on each of the 4 tables in the science room, plus several objects (below). I asked them to draw the shadows for
-a golf tee, near the light and far away
-a clear plastic cup
-an 'H', near the light and far away (I had a bunch of plastic H's, like little pieces of I-beams, that I got from something like a swap meet.)
-an animal (some cheap plastic animals, I suppose)
4. I gave them the 2 hand-outs that are attached (this was before computers!). The one with the H's is only useful as an idea, since the H's aren't readily available.
Lesson #2 is hard to convey without diagrams, but you can email me if you want to know about it.
You probably have lots of materials and ideas of your own.
Lesson #3 was about light & color and used diffraction gratings and colored paper and colored cellophane or transparent colored 'report covers' - red, yellow, green, blue. ... you can email me.

Regarding your other questions:
1. I like this poster on Women in Science and Math from the National Women's History Project:
http://www.nwhp.org/new_catalog/posters/posters3910.htm
2. I don't know where your school is located, so that affects who might come to give presentations. As you can see, my science materials, from teaching at IV school, were fairly simple. Your students can certainly ask questions over the Internet. I don't have any particular ideas about pictures of scientists or careers. I think just talking about the possibility of being a scientist is enough career info at that grade level.

Thank you for your question, and good luck with your teaching. Science teaching is so important.