Britanny lodging

I am planning my vacation (2 partents + 2 children) to France this summer and having a very hard time in a hotel booking. I want to stay in Morbihan (close to Carnac) or Loire Atlantique (close to La Baule), in other words close to the beach but not in too crowded of place.
I appreciate any suggestion. Can I simply drive there (we are renting a car from Paris) without reservations?
Thanks.
Natalia