First time poster/long time reader* I have not posted in the past since I played for the Bulldogs but I couldn't resist to help a fellow bulldawg out here.
I went twice in 2015. Once for business, the other for pleasure.
I'm a Marriott person so I used points and we stayed at the JW Marriott on Pennsylvania Ave. It was pretty sweet. The second time I went (for business) they put us up in the Capital Hilton. Either or was great due to location however, I'm not sure of your budget as both of these hotels can get pricey.
If you do choose a hotel kind of out of the way, look for Marriott's or other brands similar that are within walking distance of the Metro. You can just about go anywhere you want to go on the Metro.
Both times I flew in to DC, I hopped on the Metro to get to my hotel. We also used the Metro to get to the things we wanted to tour.
If you want to do tours, I'd highly recommend DC Tours by Foot.
http://www.freetoursbyfoot.com/washington-dc-tours/ They are free however you can choose to tip the guide at the end of the tour if you feel necessary. We toured with them through the National Mall and did another tour with them through Arlington Cemetery. I will say again, they are totally worth it. Just make sure you go on their website and set up a time before hand, like a reservation.
We also toured the White House while we were there. If this interests you, get in touch with your Senator and someone from their office will help you out. They can also assist you with a tour of the Capitol building as well. Side note - Our tour of the Capitol building through our Senator's office was just so-so. Cool that we were in the Capitol but that's about it.
DC is a foodie paradise if you're into that. That's the main reason I went. Check out Founding Farmers(go early), Pearl Dive Oyster Bar, Old Ebbitt Grill, and Ted's Bulletin. If you're a foodie, give Zaytinya a try.
Misc things to note:
-Bring your camera if you have one. It's worth it and does better than your cell phone.
-Check out the Jefferson Memorial at night if you can. It's unbelievable
-Check out Arlington Cemetery and the Tomb of the Unknown Soldier (preferably by tour if all possible)
-There's an option to take an elevator up in the Washington Memorial (we didn't do it but looked cool). You have to make a reservation ahead of time.
-Most if not all museums there are actually free so take advantage. Smithsonian, etc.
-If it's your thing, we saw a play/musical in Ford's Theater where Lincoln was shot. That was pretty cool.
I applaud you for taking your family up to DC. It's one of the coolest trips I've done. I had to constantly hold back my redneck and not grow long sideburns, grab a Pabst, and yell 'Merica the entire time I was there.