Thank you for the great suggestions! Both my children really enjoyed MIT's Scratch program, and I incorporated playing with Scratch into our homeschool plans. Wired's Geekdad does have a compilation of robotic projects for kids that use common household items, like Tinker Toys. http://www.wired.com/geekdad/tag/projects/

Instructables has a lot of great ideas, too.

Thank you!