After you've performed your investigation in opaque objects creating shadows why not show the following video...

This video is hosted by Youtube, which has a wide range of videos available. Some of these are great for schools to use, but others are not appropriate.
At the end of this educational video, links to other videos may appear. Teaching Ideas is only recommending the original video shown. Please check the content of any videos before showing them to children.

Here's another link to the video... http://www.sonnyradio.com/wonderfulshadows.html

Show it through once then repeat and narrate over it (especially the child and adult hands as near and far from the light source). My Year 6 love this clip and I have to say it is both totally engaging and moving. Enjoy!