I agree with previous poster. Washington, DC. We just got back from a two week trip ... we spent 3 days in DC. We stayed here:
https://www.nps.gov/gree/index.htm
There is an Enterprise rent a car directly across the street from the Park entrance. We rented a car and drove the 15-20 min drive into DC. It was faster then taking the Metro. And since we were only there for three days time was important for us. But it you prefer there is a Metro station available nearby.
The park was a nice retreat after a fun filled day in DC. It is very wooded. Saw wildlife (deer and fox). It's easy to forget that you are surrounded by city. The ranger station had several kid friendly activities and handouts/coloring books. And if your kids are working on getting National Park passport stamps, DC is definitely full of places to visit.
Our kids are 10 & 7 and they had a blast! Highly recommend.
Our first trip our in our 2016 Axis 25.3