I know one that nearly fits the bill...the pool is indoor though. Sea acres holiday park. Kennack sands, Lizard,cornwall. It's run by parkdean holidays...but it's very small and quiet. You can walk down through the park and on a farmers track to the local beach or there is a very narrow road down .It's also a short drive from Kynance cove which is absolutely stunning.
We stayed at one in Mawgan Porth (think it's just called Mawgan Porth Holiday Park) they have caravans and bungalows. Outdoor heated pool really clean and lovely views plus a kids playpark. Not a huge amount of open space for ball games etc but 3min walk to huge beautiful beach with sand, rock pools and a strea. Plus couple of pubs and shops, cafes on your doorstep. Very quiet at night etc so great for little children. We were very lucky as we stayed here a few years ago and had two weeks unbroken sunshine! We've never had this in Cornwall since!