OP here. Again, thank you all for your responses! To the PP: we do need a car. We are leaning toward flying Southwest out of BWI.

I cannot imagine why you would drive unless you needed the car when you got there, if flying was an option. The flight is what, less than 2 hours? Versus 10+ hour drive with a six month old? That sounds like the very definition of hell to me ...

Be aware I-81 is very heavily trafficked with tractor trailers, if that bothers you.

It's about an 11 hour drive if you make very minimal stops (for gas and drive-throughs). With little kids it will be more like 12.

We used to drive from Delaware to Johnson City, TN twice a year. It's a long drive, but the scenery is beautiful.

We did it a few years back pre-kids. We left after work on a Thursday, drove to Roanoke, stopped for the ngith, then finished the drive the next day. It took about 12 hours. We did the same thing on the way back, took 2 days to do the drive.

We do this drive twice a year. My family lives in TN. We drive down and have early lunch in Roanoke. Then we drive until we get to Knoxville. We usually spend the night in Knoxville. We usually drive until we are on the Western edge of Knoxille and at the Marriott. They have an indoor pool (for the kids to play). It is in an area with lots of restaurants, two grocery stores and shops. It also has a Wal-mart close by in case you forget something. We then drive the roughly 4 hrs to Nashville the next morning.
We have never tried to drive straight through in one day. My DDs are 4 and 6.

My sister went to Vanderbilt so we made this trip a lot. The drive is tough (we also drive to Boston often). She would only drive to get her car there and back each year. We always flew southwest and they were great. Short, direct flight. I love flying them now with kids since you can check 2 bags free, no stroller restrictions, etc. The airport in Nashville is convenient too. I would highly recommend going that route over driving!

Wow you guys are great! This is so helpful. From the responses I'm guessing flying will be the sanity saver for us. We also do the drive to Massachusetts, so the PP who mentioned that Nashville felt much longer has hit on what I was worried about. I'm not crazy about flying only because I think flying has started to become hellish for families. However it may be the best option for this trip.

I've heard Southwest is great with kids, and I see they have some great BWI - BNA fares. Has anyone else flown Southwest for this destination? Any pros / cons / tips?

PP here again. I should say that I might drive, if I went in with the understanding it might take a little longer and possibly even stop for a night mid-way. I understand the apprehension of taking a baby on their first flight.

I personally never drive if the drive is more than a few hours. I just have no interest. Maybe if I were doing some planned trip with stop sites along the way. Maybe. This is for my own sanity and comfort.

The flight is a quick one, so seems like a good starter flight for kiddos who haven't flown. The drive is gorgeous and doable in 9-11 hours, but that's what it took me as a solo adult so you'd need to account for the requisite kid stops. Breaking it up over two days would help - that's a long trek for little guys in one sitting.

If I didn't hate flying I'd probably recommend the plane just so you don't have a 2-day journey at either end of your trip. But if you choose to drive it really is nice - especially crossing the mountains. Good luck! I'm jealous love Nashvegas!

If you and DH take turns, I might drive.

DH and I just did the drive ourselves (w/o the children however) and found it felt long. Very long. And we have no problems driving to Massachusetts. The 10 hours is just right around the time when you start to hate life.

Also, in reality the trip there took about 12 hours due to some traffic. The trip back took about 11. (10 means no stopping)

I see on Google maps that the drive to Nashville from the DC area is about 10 hours. Is it really 10 hours, or is that just optimistic? If you were going from DC to Nashville with a 5 yo who is a great traveler and a 6 month old who has never flown, would you drive or fly? The 6 month old is pretty mellow, but I think it's hard to predict how babies will do on planes. I would like to drive, maybe stopping overnight in Roanoke, and DH is inclined to fly.