If you’re thinking about what to do this weekend, building a robot for your kids could be a good idea. This is not very difficult and the result is really amazzzzing. You will get a robot that can be teleoperated via WiFi (i.e. you can control it from almost anywhere in the world) or programmed using shell script for the price way less then an average robot you can get in a hobby store.
More details about the projects are here: http://andrey.mikhalchuk.com/category/robots