We loved Huntington Beach State Park.They have some full hookups and the rest are water and electric.Sites vary from open with no shade,to those in the tree that are very private. What is great for kids is the Nature Center programs or the nature walks.We were there over Christmas and they had things scheduled almost every day.It's a short walk to the beach and there's a neat large old home ,Atalaya that you can tour.
It's not too far from Murrel's Inlet where there's lot's of great places to eat.We very rarely stayed at commercial parks when our kids were young.Always state or federal parks.They never complained about not having things to do.