Science projects anyone can do with their kids, or by themselves

Crystal Radios are easy to build.  Here is a link to an inexpensive kit from Amazon
here is a link to detailed instructions for making a crystal radio from parts.

So something useful & neat, if your looking for something besides a radio, Science Toys has lots of other projects you can do.  All of it is educational, not just the science, but the skill building and problem solving required to get it right are valuable skills for learning any topic or dealing with real world issues.