This is a great idea, Paul. What a great gift! I am guessing the focus of your trip will be Normandy. I was just there in September and absolutely loved it. We went on two Battlebus Tours -- highly recommended on this site. We chose the American Highlights and Band of Brothers Tour. They were great. They have a website where you can see what the tours cover. They also offer a two-day American Exerience Tour, A British Highlights tour and Canadian Highlights Tour. You need to stay in Bayeux to take these tours. It's a nice town and also offers the Bayeux Tapestry, which I loved.
We also spent a day driving around on our own to see some of the sites that we missed on the tours. We went to the British Cemetary in Bayeux. Then we drove to Longues sur Mer (sp?) to see the German gun batteries (only original guns remaining), Arromanche (saw the 360 movie), and Pegasus Bridge.
Will you be there on June 6? If so, that might affect your plans; it may be more crowded, harder to get reservations, etc. I don't know.
It would help to know more about you and your son's level of interest in WWII, how much knowledge you have, etc. If you are really knowledgable, perhaps you don't need a tour, though I think anyone would enjoy the Battlebus Tours.
I'm not sure where else in France you might want to go. We are considering going to Belgium next year to see Bastogne and other WWII sites, but I haven't done any planning yet. You might want to consider a quick trip to London. The Cabinet War Rooms are fantastic -- the underground site where Churchill lived during the war. They've left it just the way it was during the war with maps, etc. The Imperial War Museum is really interesting too. It's an easy day trip with the chunnel, though I have not taken this myself.