BWI has its own Amtrak station with a short bus connector from the terminal. You don't have to rent the car until it is needed for the trip out to Mt. Vernon. Washington Union Station is on top of a major Metro Station.
Union Station is within walking distance of the Capitol Building.
You can also rent a car in Union Station and several other places in DC.

Here's my 2-cents worth (from a local):

Mt. Vernon -- I'm not sure I'd get tickets online before coming to D.C. because if you choose a date and the weather is crummy, you won't want to spend much time there. The tickets to tour the mansion are now timed, so gone are the days where you had to stand in a line forever to get into the mansion. I'd either book tickets once you get here and see what the weather is going to do or "bite the bullet" and get up early so that you can get a decent time for your tour.

Monuments and Memorials--Biking around the monuments with young kids during a busy tourist time (peak cherry blossoms) is not something I would recommend. Also, you waste valuable museum time when you visit the memorials during the day. I'd go after the museums have closed (5pm) and spread them out over 2 evenings--one evening for the monuments on the Mall; one evening for the monuments around the Tidal Basin. It will still be light at 5pm and by the time you finish, you may see the monuments all lit up--special!

Spy Museum--This place is going to be PACKED that week, which makes it a very "un-fun" place to be. (Voice of experience speaking.) Also, it's not such a great museum for young kids (e.g. 7-year-olds) because the exhibits require a lot of reading. I'd skip it. If you feel you really have to go, order tickets in advance to avoid the long lines and the chance they will be sold out. (The tickets are timed and only a certain number are sold each day.)

TomFuller--there is no way in this world I am Amtrakking and carrying all the butt loads of luggage required for family travel plus negotiating different trains with 2 kids who are not used to that kind of mass transit, etc. Sometimes, you just bite the bullet and pay the money. If it was just DH and me, I would go without a car in a heartbeat. That's how we have always done any major city-US or European. But I don't want to lose anybody and when it comes to family vacation, I do not pack light. I bring EVERYTHING!! As the mom in Modern Family said--I'm a mom. This isn't a vacation. It's just a business trip.

Longhorn--thanks for the info on Mt Vernon--I definitely think waiting till we get there and getting tix will be better. I really want to be flexible for weather reasons. We will be fine with cooler but being outside in the rain is no fun. And I am assuming it won't be hot or humid--humidity kills us since we are from the desert. I am thinking 60s-70s. Though my SIL said it was 40 there with a light dusting of snow in the last week! I will pack prepared!

Help me a bit more on the monuments--I like the idea of splitting it up into 2 sessions. But we would still want to do it in the morning or the kids will be too tired after a day of museums. By 4;00, they are ready for a hotel pool, early dinner, and some cartoons Of course, maybe with the time difference I can keep them out longer, but I doubt it. So do we get off at one Metro stop for the Mall monuments and then another for the Tidal Basin? Or would we take a cab from a Metro stop to the Tidal Basin? It's hard to judge distance based on the maps. Then can we take a cab from from the Tidal Basin to one of the museums? I am trying not to have to walk a long distance from the monuments to the museums. It just takes longer and wears the kids out. (and has a high probability of creating whining which frazzles mom's nerves!)

Good tip on the Spy Museum. My kids really want to see sights and then move on at this point. Maybe in a few years when they are older. Good to know!!

>> So do we get off at one Metro stop for the Mall monuments and then another for the Tidal Basin? Or would we take a cab from a Metro stop to the Tidal Basin? It's hard to judge distance based on the maps. <<

The Smithsonian Metro station (on the blue line, you'll take it from Alexandria) is the closest to the Mall & the Washington Monument, the place you probably want to start your cherry blossom and monument tour. To give you an idea of distances, it's a little over half a mile from the Washington Monument to the Jefferson Memorial and about a mile from the WM to the Lincoln Memorial. There are no metro stations around the Tidal Basin and if the crowds are heavy you'll struggle to get a cab. Walking is really the deal.

One suggestion for you that might be a hit with your kids is to take a pedi cab around part of the Mall and Tidal Basin area. You can catch them in the area or you can book one in advance. I also agree with the idea of doing some or all of the monuments at night with one of tours so you can rides between the monuments.

Also consider renting one of the paddle boats to take out on the Tidal Basin. You'll definitely want to book that one ahead of time since you're there during the cherry blossom time.

Other ideas:

Smithsonian Postal Museum - It's a great place for kids, 10 and 7 and not as crowded as some of the museums on the mall. It's across the street from Union Station which has a metro and lots of kid friendly lunch choices.

The Old Post Office Pavilion - One of the best views in the city. Other than that it's all fast food and touristy shopping. But the view is worth it.

National Building Museum - This place is in Penn Quarter and not on everyone's list but check out the website as it's got some interesting stuff for kids.

StantonHyde, there really is no way to use Metro between the monuments and the Tidal Basin. And a taxi will be stuck in all the traffic of those silly folks who want to drive by the blooms. The idea of riding bicycles to tour the monuments is good; however, during your visit the crowds around the monuments will be heavy and could dampen the cycling experience.

With "peak" blossom time scheduled during your visit, I would also suggest not even trying to walk your bicycles through the crowds. Some paths along the basin are narrow and without guard rails. Crowds are dense, with most people looking at the flowers instead of where they're going.

If you can get the family up and out early to see the blooms, then take your bicycle tour, that can work. We've done it quite a few times with success. The museums all have bike racks, so it's easy enough to secure the bikes should you want to visit a museum.

A note about the Zoo. Take Metro to the Cleveland Park station and walk downhill to the Zoo. When leaving, walk downhill to the Woodley Park station.

We cycled around Washington with our 9 yr old for 3 days. It was AMAZING but it was December so the crowds weren't too bad. I loved the rent a bike system & you can download an app on your phone to show you were all the racks are. My only issue was that there were no helmets supplied (it's illegal to ride without one here in Australia). Next time we visit I'll take my own.

If you aren't on bikes the distance between monuments is further than it seems ( especially for little legs). I'd do it in two separate stages. Don't leave out Arlington Cemetery. The changing of the guard is awesome.

I would also recommend the Air and Space Museum. Worth at least a few hours. Some amazing planes, etc

If you want to see the Spy Museum, you might do that for half of your Zoo day. The Zoo isn't very large so you should not need a full day to take it all in. Then take the Red Line to Gallery Place, the station one block from the Spy Museum. Or the Spy museum first thing in the morning, then all afternoon at the Zoo.

The cafes at the Natural History Museum, the Baltimore Aquarium, and the Museum of the American Indian are all fine. Pretty much on par with most European museum cafes. The on-site dining options at the Zoo, however, are horrendous!

Find a sandwich shop, deli, or small grocery near your hotel and PACK A PICNIC on zoo day. Otherwise, there are a few family friendly restaurants just outside the zoo on Connecticut Ave. There are no food trucks near the zoo.

Sound advice from fourfortravel above on how to best Metro to Zoo - you'll do enough hills in the zoo itself!

The earlier the better for the Zoo!!! In the early morning (8am-10am) all the animal youngsters are out and about playing. The zoo is not an all day trip. An ideal trip would be 8am-noon and then have lunch before getting back on the Metro.

Bikes for the Mall - excellent idea!!! If you choose Bikeshare, then you have to park the bikes at an official Bikeshare station. If you choose another bike rental company, they give you bike locks and you can park the bikes pretty much anywhere (like at the tidal basin). Both are good options but something to think about. Research both and see what works best for you....

Before I suggest restaurants near your hotel...which Alexandria Residence Inn is it - Duke St. or Mill Rd.???

The OP started another thread with a specific question about restaurants. (http://www.fodors.com/community/united-states/alexandria-kid-friendly-restaurants.cfm)

These were my suggestions:

In Old Town:

The Majestic Cafe - The food here is upscale comfort food and is usually rated one of the best in the DC area. You will definitely want to book here and now wouldn't be too soon.

Eammons - fish and chips. Who wouldn't love a place whose motto is "Thanks Be to Cod."

Union Street Pub - nicer pub food and some really good seafood dishes. They have an oyster bar.

Pizza Paradiso - excellent pizza but they don't do reservations and lines can be interminable. Might be better for take away to your hotel.

Nando's Peri Peri - Peruvian roast chicken and chips.

Rustico - great pizza, burgers and salads.

In nearby Del Ray:

The Del Ray Cafe - This place is run by the owners of a long standing high end french restaurant. It's a great opportunity for mom and dad to have something a little nicer but in a casual setting with a very suitable kids menu. Definitely book here. Also save room for dessert b/c a block away is the Dairy Godmother, home to real frozen heart stopping custard.

You'll also have a Balducci's and a very nice Whole Foods available, both of which have great prepared foods. There is also a Trader Joe's in Old Town.

<<<If you choose another bike rental company, they give you bike locks and you can park the bikes pretty much anywhere (like at the tidal basin).>>>

Other bike rental companies give you helmets, too. It's just a different setup. Instead of taking a bike, returning it and then taking another (Bikeshare), you just rent a bike for a number of hours. Look at bikeandroll.

We have been to Air and Space at least once if not twice, so that is why we are not hitting it. We will see if the zoo is really half a day. My kids love animals. But good to know to have something in my back pocket for that day if needed. Thanks for the tips on the hills too/from the zoo. I remember that now from last time! Thanks for the restaurant ideas. I posted in Va too in case people were only looking there.

Re. restaurant ideas--We are staying at the RI Duke Street.

Thanks for all the feedback on seeing monuments. Looks like we really need to walk. sigh.

Looks like you have a pretty good plan so far. The Baltimore aquarium is pretty cool, so if your kids are into animals they may really enjoy it. Walking around the rest of the inner harbor area can also be fun... rent paddle boats, visit the ships, go shopping, have lunch, etc. You could also work in a visit to the Science museum or tour of Camden Yards if you have baseball fans. So you could definitely make a full day of it if you end up visiting Baltimore. Have fun!

Very family friendly dinner ideas a quick walk from your hotel. Starting with my top suggestion:

http://www.eamonnsdublinchipper.com Fresh, perfectly cooked - excellent for families with good kid options even a grown-up would find tasty.

www.austingrill.com Full Tex-Mex menu

http://www.hardtimes.com Excellent chili plus full menu of American fare.

http://www.redmei.com - Very good but "Westernized" Asian food (Kung Pao, Pad Thai, Sweet & Sour, etc.) nothing kids will consider "weird" like duck tongue or snake...

StantonHyde~have you been to the Air & Space Museum near Dulles? It's less crowded and has different exhibits. My nephew, who was in an aviation phase, loved seeing the SR-71 and the Space Shuttle.

Another thing you might consider is the Duck Tour. My daughter and my niece and nephew were around the same ages of your children when they went, and they loved it.

What about the paid bus tours for the monuments? The 3-4 hour ones that you are able to get off, explore a bit, get photos. I add this as a suggestion to StantonHyde, but also as a question for our trip in June. My children are older and we were seriously considering the evening tour, too late for StantonHyde children.

I am not a tour bus person. Like no way in heck. I know, my loss I would consider the Ducks tour though, just because I think its' funny.

If you do the Duck Tour, I will warn you~the children get souvenier whistles shaped like duck bills.........

I am not either. But with the crowds thought it might be a good alternative, also a bit of an ease on the volume of walking. I have been perusing the post for DC trying to make our itinerary for June. Please post after your vacation, would love to hear how it went!

Dont take a bus tour during peak times. Too much traffic and therefore you will be sitting in it going nowhere

Yep, I think we have to suck it up and walk. Duckbill whistles. hmmmm, somehow mommy might have to assist them in getting "lost" on the Metro.........

I did enjoy the Duck tour I did in DC. You dont get the quackers until after the tour