We really like Jellystone Park at Marion, NC, near I-40 east of Asheville: jellystonemarion. We visited there with our 8 & 11 year old grandchildren this year after a great time the year before. Their water slide is fantastic so the kids spent lots of time there. But they also enjoyed the planned activities--gaga ball, goodnight to Yogi campfire, movie with new friends they met, dance for kids, pool, mini-golf, etc. We've also done the one in Missoula, MT, and one in IN with them in past years and all have been really good for kids before teens, at least. We are looking at the one in Fremont, IN as potential for next summer. It has won many awards.
Extra cost for all the kids stuff is worth it in our opinion. Lots of activities are included with the price. Going mid-week may also reduce cost.