Kiln Park is in Tenby and has access to one of the excellent beaches, it a "all singing and dancing" park ie pools, entertainment, restaurants, amusements etc....
Alternatively, there is Tudorglen Park, between Tenby and Pembroke, is smaller site but it does have it's own pool
If you are looking for a cc site in Pembrokeshire we can recommend Freshwater East, very popular with families and from the site its a short walk across the beech car park to the beech. Easy drive to park and ride at Tenby.