How far away are you willing to go?

The national museum of the Marine Corps in Quantico is excellent.

Bump

The GW Masonic Temple in VA

Cryptology Museum then go to Dave & Busters at Anne arundel mills mall

I second or third tubing in Harpers Ferry.

Beaver Dam Swim Club

Or other swimming holes

https://www.washingtonian.com/2015/07/27/6-great-swimming-holes-near-washington-dc/

Sandy Spring Adventure Park in MD is a great suggestion. There is another tree top ropes course now in Fairfax County, at South Run Rec Center, not sure how it compares.

Flight Trampoline Park

My kids love amusement parks so I would recommend 6 flags and King's Dominion. If one is a favorite and you are really free a few weeks then maybe get a summer pass. I don't think they are that expensive.

We also go bowling a lot in the summer because it isn't crowded.

Sandy Spring Adventure Park
Terrapin Adventure
Hiking in Sugarloaf
King's Dominion

OP here. Thanks so much for all of these great recommendations!

Go for a hike at Scot's Run, Great Falls, the canal tow road, Roosevelt island.....
Rent kayaks at Key Bridge Boat House or canoes at Fletchers's
Go to a National's Baseball game
Make the trek to Udvar-Hazy
If you want a day trip- Luray Caverns or Shenandoah National Park or Inner Harbor in Baltimore
Mount Vernon
If you have golf clubs, golf at Haines Point

ZavaZone
ClimbZone
Monster Golf or Galaxy Golf
Harpers Ferry Adventure Center
Adventure Park USA
Laser Tag

National Arboretum

Far away but can be done as a full day trip - hike Old Rag Mountain on a weekday to avoid the crowds.

These are an hour out, but what about:
Paintball
River float on the Shenandoah River

-Putt putt golf or just hitting balls at Top Golf of someplace similar
-Sailing lessons on the Potomac (or sailing camp)
-Walk or bike the C&O Canal
-Go watch a minor league baseball game in your area
-Go fishing

Looking for some fun things to do with my boys in and around DC during the few weeks they won't be in camp. We've hit most of the more popular DC sites and museums so I'm looking for some new/different suggestions either in the city or within an hour or so drive. Thanks in advance for any suggestions!