M.P.
Charlotte has some attractions for kids- Carowinds is a theme park located in Charlotte. Also, the Nascar Hall of Fame is located there as well (if your kids are fans). I know there is white-water rafting tours in Charlotte and I know they have family (beginner class) rapids for families with kids- I think that would be a total blast!
The closest beach is going to be about a 4 hour drive (Wrightsville Beach or Myrtle Beach, SC), so plan to stay overnight if you go.
You might consider visiting the Blue Ridge Mountains. Chimney Rock is fun, Linville Caverns, Grandfather Mountain, Biltmore Estate (as someone else mentioned), etc...
Hope this helps!