The Lancaster area of PA is so pretty! They would enjoy that - and would have to have their picture taken under the town sign for Intercourse, PA! I'm from Texas and it takes hours to get anywhere here. But in PA you have Gettysburg and Philadelphia for history people, Lancaster County for different culture people, Hershey for chocolate people (Is there anything there still to see? Hasn't the chocolate factory closed?) My husband is a train buff so we went to several train museums there, too. Not far to Atlantic City from there.
My daughter and son-in-law lived in the DC area when he was in the Marine Corps. When we'd visit them we'd go traveling around for a few days, then stay with them for a few days, then off again. I was amazed at how many things we could see without driving for days and days!