We are thinking of heading down in the middle of March and are look for places to stay that do not allow children. Any suggestions?
So far as I know there aren't any "adults only" properties. The Anderson is probably the closest you'll find because it doesn't have much in the way of amenities that would attract families. You might look at the new Hilton 22 as well. Also be aware that the annual "Run to the Sun" car show runs from the 15-18 so it may get a little hectic especially in and around Broadway at the Beach.
Myrtle Beach is VERY family friendly. No adults only hotels there at all. Having said that....you might not find many kids there in mid-March anyway. Maybe some college age kids there on Spring Break. And golfers.
If you do still want to stay in MB, I agree with the hotels mentioned above...Anderson..or Ocean 22 by Hilton. Island Vista is a very nice hotel in a very quiet section...no hotels on either side. The water features are what usually draw the kids, and none of these 3 have big water features. (although the weather may still be on the cool side for outdoor swimming anyway)