London's workable, it's a great hotel and well situated.
Places I'd suggest not missing are Hampton Court Palace, Tower of London, London Eye, depending on your son's disposition they do a great "ghostie" tour around the city of London as well as a Jack the Ripper tour. Some 9 Y old's love the ideas of ghosts and blood and gore, some are'nt ready for that, you know your son's level of ability better than anyone.
Travelling from London to Paris I'd strongly recommend using the Eurostar train service, it's much quicker, more comfortable than flying and it's a unique experience to say you went under an ocean in a train.
Paris depends a little on how much time you want to spend in DLP and/or Paris city itself. The points deal at DLP is pretty good if you're 3 or more in the room as you get tix and breakfast. The other advantage is the style of room you'll get is pretty close to what you'd be used to getting in the US.
They run a pretty good day tour from DLP that takes you round a number of the "must do" attractions in Paris (Eiffel tower, Notre Dame Cathedral and a Seine river cruise). It's an excellent way to cover the bare minimum of Parisian sights. The train service from DLP to Central Paris is excellent, as well as there are direct trains from London Waterloo to DLP.
IMHO Rome is just the most incredable place in the world to visit, if you're on limited time ( and a week is limited) I would plan to base yourself in central Rome ( I think most of the
DVC offerings are not in the city itself) and cover all the wonderful sights of Rome. The only time outside of Rome you could try a coach trip from Rome that covers Naples, the Amalphi coast and gives you 3-4 hours in Pompeii. I did this trip a few years back, it certainly was a long day, 6:00 Am pick up and didn't get back to the hotel until after midnight, but Pompeii is just one of the most amazing things you will ever see anywhere.
The resorts in the countryside are spectacular, but if the point of the trip is to try and cover a good portion of the amazing history of Rome you may be better served by taking a resort in the city and not lose time in transit. Traffic in Italy can be a major challange, but most of the main sights are in walking distance of the city center.