About two years ago, my then-9-year-old and I worked on a cool project to program Lego Mindstorms to fly a RC plane, which we cheekily called a Lego UAV. (And were then, even more cheekily, accused of "weaponizing Lego"--UAVs are export controlled as weapons!) It worked, amazingly, and was a lot of fun.
Then, as sometimes happens, I got obsessed, while he moved on to other things. In the past two years, I've made cellphone UAVs, Basic Stamp UAVs, autonomous blimps, and a true gyros+acellerometers+GPS autopilot version of the Lego Mindstorms UAV that's now in the Lego Museum in Billund, Denmark. We set up an amateur UAV community at DIYDrones.com, and get thousands of people each day exploring this new dimension of aerial robotics.
Now this project has gone pro. Our first commercial autopilot, the Arduino-compatible ArduPilot, has been released and our goal of taking an order or two of magnitude out of the cost of an autopilot has been achieved: it's $24.95!
Combined with a RC plane, this makes it easy to build a complete UAV for less than $500, which is really kind of amazing. As exciting as that it is, it's also sobering to know that a technology that was just a few years ago the sole domain of the military is now within the reach of amateurs, so we spend a lot of time educating our community on FAA regulations and safe and responsible flying (always under 400 feet, stay within line of sight, pilot always able to regain control).
As for my kids, well, the technology pretty quickly went over their head (in all senses of the word), but they're still involved a bit: video taking, pointing the ground-based telemetry antenna at the plane, laughing at Dad when his plane crashes and being bribed with ice cream if they'll tag along for yet another test flight. Someday, maybe one of them will want to get involved with some aspect of this again--programming, hardware design, even piloting. But until then, this counts as another project that started GeekDad and ended all Geek ;-)