Do something silly like find a cheap ticket somewhere like DC and go for the day. Call it a birthday present. While in DC go to the Smithsonian and see the Space exhibits and some other fun thing. Fly home.

Make sure you stop by the cockpit and let your son talk with the Captain before taking your seats. And if you fly to DC get a window seat on the left side of the plane going down and the right side going up so he can see the eastern seaboard.