In my personal opinion, Isle of Palms or Sullivan’s Island are better than Folly Beach unless you are a teenager, a drinker, or a surfer (which isn’t always the case when bringing a big family):

http://charlestonscvacation.reachlocal.com/

Here is a good link for rental companies. There is a link for Wild Dunes on this page, it is a great little gated community with beach access, pools, activities, etc.
http://www.sciway.net/tourism/charleston-sc-vacation-rentals.html

GOOD LUCK.