Sounds like a nice drive. Have you done distances in the car with children before?
My experience of driving with small children is that they appreciate the distinction between scenic and non-scenic as different versions of hell. And they don't hesitate to communicate their unhappiness. I take whichever routes are quickest and offer interesting breaks. But the driving is in no way enjoyable for them - only the arrivals.
If you have those miracle children that like being in a seat immobile for hours on end, then the world's your oyster - just meander along the green marked routes on the Michelin maps. You're never so far from an auto route if you want to get a move on.
Small tip: plan to lunch at shopping malls. Although, I hate to advertise this souless feature of modern capitalism, they do have their uses: invariably there is a cheap supermarket fuel outlet, chemists, big supermarkets full of good produce and low priced restaurants, as well as McDo and Quick of course. Lots of a/c can be a nice relief as well. They tend to be easily found on the edge of town too. Avoid on Saturdays though.
Fast food outlets in malls invariably have big padded climbing frames/jumping-about-like-a-mad-thing areas. Again, fast food joints are probably not what you are looking for in your French experience, but grown-up restaurants are difficult places for most children. And a testy "sit down Harry I won't tell you again" after hours in the car aren't ingredients for happy holidayers are they?
Big supermarket names include Auchan, Leclerc, Carrefour and Super U.
Here's a link to fuel stations in France that do LPG ("GPL") you can use to track down supermarket fuel stations.
stations.gpl.online.fr - Annuaire des stations GPL françaises
...I can't actually believe that I have just recommended malls and fast food to a traveller.
Children do alter your options alright. (French people holiday in big family camper vans to get around these issues.)
Around the world 2000-2004, on a 1993 Honda Transalp