Just another thought, Camping Ranc Davaine, although not along the Ardeche itself, is a large site, with the most fantastic pool complex. Slides, fountains, rushing streams, whirlpools, etc. It also has a great restaurant and pizzeria. There's a smaller river adjoining the site, where you can mess about in canoes. It's great for kids, with lots of activities. It can get VERY HOT in high season, but they have a 'mist' system, which sprays cooled water mist across the outside bar/restaurant area - sounds dreadful, but fantastic when it's very hot.
There are several sites in this area which accept Camping Cheques or ACSI card, which make it great value outside of the mid-July/early August season. Ranc Davaine is one of them, as is Les Ranchisses at L'Argentiere. I think Sampzon accepts ACSI or Touring Cheques - can't remember which. We've stayed in the Ardeche from about 18th August, and used Camping Cheques - but haven't checked out the site acceptance dates this year.