We have just come back from Switz trip would recomend stopping on route especially to give kids a break. They may well enjoy the camp site at Verdun. Named "Verdun" They have a swimming pool and good facilities, and this is about half way to interlarken, believe me you should enjoy the getting there as well as the arrival, arrive fresh ! Have a good trip.
------------- forest fan
Don't forget to leave a review of the French and other European campsites you have visited!
Not sure on the geography... but La Fayolan in the Jura is a nice site with lovely pool complex, and we did it from there to Milton Keynes in one hit no problem, so would be easy from Ashford.
Stayed in a Canvas Mobile Home this year in Manor Farm, no problems. Living area a little tight and main bedroom the same but nothing to worry about. Mobile Home was a good choice too - we had thunderstorms every evening for 12 days. Temperature didn't go below 30, that was in early July. We only used the car once during our stay, used free buses and the trains / boats the rest of the time.