We had to to keep going back to this site as part of our long summer holiday when our kids were around that age. http://www.lesmenhirs.com/
There was always plenty of entertainment and pony riding etc for the kids and the pitches were all mature and well screened even then and it is a short walk to the beach.
Carnac is busy at night time with loads to see and entertain the kids if you just want to wander out from the site. And the port at La Trinite sur Mer is just along the road as well.