I do france in the May bank holiday half term and Cornwall in teh summer hols
I also vote Vendee in France, great beaches, but less to do if it rains (bear in mind this is lateMay/June) in the summer the weather is supposed to be fab. I would defineatly recommend Vendee. We also did Soutern Bittany - Carnac a few years ago. Really lovely beach, near campsite nice smallish village (we had a pushchair and it was fine) We stayed at Camping de Menhirs Brittany which was OK, and near the beach. There is a better campsite other companies use, but it is a couple of miles inland.
When we did the Vendee we went Le Clays Plage and I would highly recommend this one. Near a beach - walkable, and lots of nice cycling around.
Last year we went to the Loire (again May/June) and we are going back this year hopefully, as there was more to do without being reliant on weather. Chateau des Marais
I also want to try the Il de Re as it looks beautiful Il de Re You can fly to La Rochelle with Ryan Air and let him pick you up there