Also, don't want entertainment etc - although a pool would be nice - but not urgent. Just a basic site where the children can ride their bikes on site - with space around the tents or in the middle of the field to play ball games etc.
Camping within the trees would also be nice.
Don't forget to leave a review of the French and other European campsites you have visited!
We had a great time here http://www.ukcampsite.co.uk/sites/details.asp?revid=7197 last year, near Saumur in the Loire. Small site (70 good sized pitches), nice enough 1.5m pool and a paddling pool, in a little bit of woodland in a small village (with lots of vineyards), football field, playground, etc. Great zoo and a SuperU at Doue-la-Fontaine a few mins away. Not 100% sure about bikes, but I think I saw a few being ridden around the site. English owned site. Usually the region for the start of good weather.
Areas - I would recommend the Vendee - great for kids, nice climate - very sunny normally and the sites are mostly in pine forests. Great beaches too, and far enough to be warm. If it's too far to do in one trip (I think it is if your kids start to moan after a few hours like mine) then you can stop overnight on route. As it's your first time I recommend you have a look at Eurocamp Independent. If you book with them they will sort out the whole booking for you including ferry, you have the use of kids club, couriers etc, when you get there and best of all you can book their ready erected tents for overnight stays.You also get a set of maps,route plan, etc. You'll pay a little more for this service, but it's an excellent way of doing it for the first time if you are a bit unsure. Check out their website/brochure, even if you don't book via them you get a good feel for the kind of sites you like and distances, etc. You can order a brochure through the website.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.