In March, what about Los Angeles, nice warmer weather, ocean, Disneyland, and mountains within driving range? Since time is limited I would fly to LA and spend a few days there, then maybe rent a car drive to the Grand Canyon, Hoover dam are etc.
I don't know if you plan on flying though. My dad once took us on a 6 day vacation and drove from OKC to LA and back. That's a lot of driving though and even a little more from AR.