My daughter and I are planning on getting a lego robot and experimenting with it. Here is a video some teacher put together of her students working with them. This video is from TeacherTube, and I wish I knew more about it, other than this looks fun.
Just as the teacher/narrator says, there are lots of principles of math involved, most of which are not that advanced, even for young kids. This strikes me as a great way to increase interest in math, programming and engineering in school kids.