Re:
Now...I don't do camping, Or actually my back doesn't do camping! However, If your family are the outdoor-sie type and fancy something a little different to the norm, then I can highly recommend Huttopia,
http://www.huttopia.com/en
Last year the other half had some meetings with clients in Rambouillet, just outside of Paris. I had a little spare time so we thought we'd make a little break of it and take the bikes, we hadn't decided on a hotel but thought we'd sort something once there based on the surrounding area and riding potential, which is when we discovered Huttopia.
It was the perfect solution! Having spent a lot of time myself in hotels travelling for work, It was actually a revelation having the best of both worlds and surrounded by beautiful scenery, great trails and it was actually a fair bit cheaper than a nice hotel, especially if you use their preferential discounts for staying (X) nights...... I would honestly say that it never felt like a compromise and more a different experience, a really nice one at that.
Essentially you have a Chalet/Chalet style huge tent for 5 people with separate rooms and all amenities (Clean toilets, Hot showers, Towels, Barbecue, Memory foam beds, Electricity, Internet access, Fridge, Gas Barbecue/grill, Garden area with seating/table, Cutlery, Cooking utensils, etc.....) all the conveniences of a hotel but in the forest..... and a stones throw from trails!
Next time we go were only taking ourselves, clothes, bikes and going to be sans car! Train, Eurotunnel, Train, Ride (the train station in Rambouillet is just a short ride) then when you get there everything is provided, there's even a swimming pool! and it's only 10 minutes from town and the supermarkets.....
They have a few locations in France and Canada...... Just not sure on the Beach/Climate front...... as there certainly weren't any beaches in the Forest, but other locations may fit the pre-requisite.