I love Myrtle Beach. There are a ton of kid-friendly stuff to do, even more for teens (Broadway at the Beach, NASCAR and Hard Rock amusement parks, etc.). It's kind of like a mini-Orlando with a big beach nearby. Also, great and relatively inexpensive golf.
I particularly like the condos/ timeshare rentals in N. Myrtle Beach. They have some high rise buildings with great views, lazy rivers, kid activity rooms, and large pool complexes. But they are away from the hustle and bustle of the Boardwalk and the seedy elements of a typical beach town. The sand is much harder than it is in NJ or MD, but its still fun to be on the beach.
This resort is my favorite, but there are dozens of similar places.
www.seawatchresort.com