(Spoiler Alert)
At the end, there's mural or placard that says something like: Most exhibits in this museum are here because of failure. The best spies are the ones you never hear of.
You could also go south of DC about 30 minutes to Warrenton, where the cold war museum is. It's also free and run bY Francis Gary Powers Jr.
The Spy Museum has better flashy interactive exhibits for kids, but underneath all of the sound and light has a _very_ impressive collection. The National Cryptologic Museum is, as one might expect, more focused on the cryptography side of things as opposed to the more general spycraft collection in both the Spy Museum and the CIA's museum, and is a better one if you're particularly interested in ciphers and codebreaking. The Spy Museum & CIA museum have more exhibits of hidden microphones, weapons, communication devices, etc.
The German Spy Museum (Deutsches Spionage Museum) in Berlin is also quite good and also good for kids. It is, unsurprisingly, particularly deep in Stasi-related materials. They have a fascinating exhibit of a car whose door had been filled with infrared lights for taking covert nighttime photographs, at really mindblowing cost.
Also note that the NSA's collection has an online portal: https://5099.sydneyplus.com/final/Portal/Default.aspx?lang=e....
And the CIA Museum's collection is partly online: https://www.cia.gov/legacy/museum/
(Sorry. I don't know how we became spy museum fans but the kids adore them. :-)
These days, online mapping and Streetview snapshots could be exhibited in a museum of street surveillance.
https://blog.google/products/maps/street-view-15-new-feature...