Hello there, I've travelled a lot in Franc and towed many miles there, my most useful advice would be to travel on Motorways if you can, they are better for saftery reasons, you're more likely to be distracted if you pass through towns.
Most towns have municiple camp sites, these are good quality sites, not the best but very acceptable.
Eat local food, that's the cheapest way of feeding yourselves, buy bread, cheese and local fruit and vegs and you'll save a furtune, don't go for the usual british stuff like Hienz baked beans etc etc.
"Touts Directions" means through route for when you get into any town or city centres, but avoid if you can.
Portsmouth-Caen is about a 6 hours crossing, the place where you are going will be a few hours drive, count on about 4 but the more you stop the longer it will take.
I've travelled with groups before and it can be a real pain in the arse, even with family, in all our travels we found the best way to go about it was for all to have C.B radios.
Also all fill up together, have everyone go to the bog, eat, drink together, then set off together, when the first car needs to stop for juice all stop and all fill up again, go the toilet etc etc, this way you can usually travel for 4 hours then stop for food, drink, shower bog etc etc, only when everyone is ready to go, move off, don't foget that if you travel on the motorways there are overnight stop over points and the facilities are usually good, with play areas for the kids, showers, restaurants and so on.
I've driven with young kids all over Europe and this was the best routine to get into, I drove to France, Spain, Switzerland, Austria, Yugoslavia, Portugal, Italy, Belgium, Germany and more many times.
Have a good time,
Cheers,
Ron.
