Need some ideas!!!

I need your ideas! I'm starting to get active with the Society of Women Engineers here in Boston and I've volunteered to keep an outreach event going where we educate kids about engineering through a FUN day filled with a variety of hands-on workshops.

I need your help with any good experiments or activities kids would be able to accomplish within an hour, BUT still incorporate learning about different engineering disciplines. We're hoping to have them complete about 6-7 different workshops for the day. I have some ideas (bottle rocket launching, music box kit, etc.)and I've looked around online, but does anyone have some good ones they really like out there?!?! If you have recommendations, it doesn't matter what age group/grade. We'd like to host an event for 3-6 and 7-12 graders. I'm open to all suggestions! THANKS!