Formed by the meeting of the Garonne and Dordogne rivers the estuary flows into the Atlantic Ocean at Royan. The is the largest estuary in Europe and is home to the oldest lighthouse in France - The Cordouan Lighthouse. The estuary itself includes an archipelago of nine islands, some are accessible during the tourist season on cruises leaving from Blaye passing alongside beautiful chateaux's. It is possible to take a trip to Rothchilds and pick up an investment.
There are many charming villages along the coast road which offer a wide variety of fresh fish as well as the usual pizza etc.
Mortagne is a lovely place to visit with yachts and a couple of lovely restaurants. I would definitely recommend it for a relaxing couple of hours.
Talmont sur Girdone is another recommendation; an ancient village in France's "most beautiful villages" category with narrow lanes strewn with flowers and little shops and restaurants to pass the time in. There are fantastic views over the estuary and on a Sunday there is a brocante. Parking can get busy peak season due to it's popularity but it is only 2 euros.
I understand you can go kayaking near Talmont on the estuary and with some fascinating fish to be caught some might enjoy a day out fishing there.
St George de Didonne is a larger resort with palm trees and great beach. Before, the water is safe but looks silty which can be a little off putting for the children. It is still worth a visit though with a lovely Californian style atmosphere.
Mescher is charming with a small centre to the town. I would drop down to the beach. It is a small and untouched cove - a gem.
Blaye is a great visit - particulary on Saturday when you can enjoy the local market wares and the wonderful medieval citadel overlooking the estuary is spectacular.