I’d agree to shorten the route unless you are going for the driving. We did 7 weeks in Europe and managed 7,500 miles and 17 countries.
The struggle we had was not rebooking campsites and even knowing where they were, you can spend a lot of wasted time trying to find them and book in, so my advice would be to plan your accommodation in advance (not necessarily book but have an idea of where).
Cities are great but bear in mind you have a car, many cities you will end up parking on the outskirts as getting close to the centre and finding parking is difficult and expensive.
Avoid the toll roads, you see so much more of the countries you are visiting and the smaller towns.
As a suggestion for your time how about the west coast of France, into Andorra (hire bikes and ride the bike park) and into northern Spain? Great views, weather and food.
Most of all enjoy the leisurely pace and time with your son, we enjoyed it so much we did it twice!