One of the things my brother loved to do, as a child, was to take things apart to see how they worked and then to try to put them back together. Although he usually took apart things that he wasn't supposed to be using as play things, like the VCR or Hair Dryer. As an adult he loved to work on cars, mostly by taking things apart and then putting them back together with some parts left over! Oops!
My point is that he was very inquisitive, as many children are, and was always looking at things and wondering how they worked. He eventually turned that into a career in Research and Development.
Remembering a time when he took apart my clock radio gave me the inspiration to bring in a few old appliances and some tools for the kids to tinker with. We had a group discussion about the tools, I demonstrated their use, and we talked about tool safety. I then set out some appliances, with their cords cut off, for my little friends to take apart and tinker with. Several kids lost interest in it almost immediately, but those mechanically minded kids had those appliance apart in no time, examining each item, setting out their pieces on a tray, and even trying to put things back together again. Of course, I admonished them not to use tools or try this on anything at home without Mom or Dad's permission.
One boy was so interested he begged me to bring in something with a cord so that he could see if he could take it apart and make it work again. I explained to him, and the others, that I cut off the cords because putting something back together incorrectly could be quite dangerous and might cause a fire. That led us into some intricate discussion about electricity and how that worked and they came up with some amazing questions that we had to go to the computer lab and research to find the answers.
If you decide to do this....
- Bring in only basic appliances with no batteries fuses inside.
- Remove cords so that they can't get plugged in and start a fire or electrocute.
- Teach tool safety.
- Closely monitor the activity.
- Encourage girls to try it out as they may feel like it's a "Boy Thing".
I found this great blog post about taking apart a stuffed animal to see how it's put together. This would work great if your kids are younger and couldn't work a screwdriver or pliers. Click on the photo to go to
TinkLab and check it out!
TinkerLab is a great site with lots of activity ideas. Bookmark it or sign up for their newsletter to get lots of ideas!
Steve Irwin Day 
I've recently found this site called The Kids Should See This. It's a great site with images and videos that kids would love and become inspired by. They have found a lot of amazing videos that would fit into any of your themes or just something cool to show the kids as a reward or a way to get the crowd calmed down. You can subscribe to the site and they will send you a weekly email with lots of fun!
I love this project because it is easy for all grade levels. Basically it is ONE line that does not cross over itself. Straight, squiggly, curvy, whatnot, just cannot go over another line and should fill up the page. Once the page is full, draw some geometric shapes and chose similar colors to color each shape. 
