Hi
I have stayed on a site at Burton Bradstock in Dorset (Jurassic area) and its wonderful for most of what you are looking for. It is right on the beach and has an area of water created by the banked beach which forms a sort of lagoon which the kids love playing in on inflatables etc as safer than the sea. Lots of great walks around and lovely scenery. While we were there we were kept awake all night one night by an eerie noise which we discovered in the morning was a donkey in the adjoining field giving birth so kids loved the baby donkey even if we were glad they didnt give birth every night
Hope you have good weather and then anywhere will be great
Linda