Would someone be able to give me some ideas on how to get from Reagan airport to Baltimore/Washington airport without a car?

Metro has a station right at National Airport. Take that to Greenbelt station, then the B30 express bus tp BWI.

Go here for all the information including the timetable.

It will be cheaper if you get a rail to bus transfer coupon from one of the machines.

http://www.wmata.com/metrobus/b30_brochure.cfm

Thanks! One more question. I am bringing a 10 month old child. Will it be a pain trying to bring a medium sized stroller on the Metro?

The feasibility of a stroller depends on the time of day, and whether the elevators you need are running that day. Do not attempt a stroller during rush hours on weekdays; the trains are so packed, the Metro is one of the few systems in the world that is actively seeking ways to discourage ridership.

There's also Metro or taxi to Union Station and then MARC train to BWI depending on your schedule.

The bus is a better option but Union Station isn't a bad way to break it into two legs for the little one or get a quick bite.

"Medium" strollers aren't too bad. I saw one the other day that was so big it filled (and blocked) the whole aisle. Try to avoid the mid-point door on the cars and use one of the end doors.

Note that the MARC trains don't run on weekends, and also they do not go to the BWI terminal as the B30 bus, you must get another shuttle to the airport after you get off the train. Between the shuttle and the transfer from subway to train, the MARC/Union Station alternative involves a lot more schlepping. Also, the B30 buses are adapted for luggage and the MARC trains are not.

I know you're a big proponent of the bus, Anon, and as I mentioned, it's a better option usually. I've used it several times and one of them included an unairconditioned hour spent in stalled traffic . . . with a child about the age of the OPs . . . and plenty of stress about missing my check-in time.

The tot wasn't having much fun and, partially because of that, neither were any of us.

Not much fun, and while the odds of a repeat are long, it's tainted my view of the bus. That's why I usually grab a latte at Union Station and relax on the more comfortable train.