NJ3rdRail, at various times in recent years I've ridden both north and south on all segments of the Crescent from DC to NO, but not north of DC, so I'll only comment on what I know. Also, I think most of what I can think of has been mentioned in various other posts, but here are my thoughts.
First, the direction you're traveling obviously makes a big difference as to what you're going to see (in daylight and/or while awake!), and I don't think I ever saw whether you'd be returning the same route or not. Assuming you're only traveling south, then you'll likely miss most of the rolling hills of Virginia. Hopefully, though, with Daylight Savings Time imminent, you'll at least get to enjoy Northern Virginia. Virginia is generally quite lovely (not spectacular, as you and LI Loco figured out, but certainly pretty). There will be several river crossings, sometimes from a high elevation, and the scenery is mostly trees and hills and farms. This time of year, with the leaves just coming out and probably some trees in bloom, it should be very nice.
You'll be coming through my neck of the woods (NC-SC) during the night, which is fine; though sometimes interesting (particularly in NC) from a railroad point of view, there's a drop-off from Virginia.
It is indeed interesting to watch for the MARTA tracks snaking past the route as you come into Atlanta. After so long in the smaller cities and towns, the suburbs of Atlanta will seem to stretch on forever.
In Alabama in particular, there are a surprising number of hills, sometimes steep. I recall there being a tunnel or three along this route, as the line plows through ridge after ridge. Watching the train snake back and forth is fun, though the curves tend to be blocked at times by hills and trees, unlike wider turns that seem to me to be more prevalent in other parts of the country. One other highlight in here is the giant army depot near Anniston, I believe it is--I recall army tanks and all kinds of other equipment lined up here, and although your view is partially blocked, it's still neat to see the stuff sort of out there in the middle of nowhere. I think that's on the right side headed south.
One final scenic highlight sort of referenced before but not really: as you approach New Orleans, you will cross Lake Ponchatrain, but in addition, you hug the lake for quite a while (lake on your right, I believe) on a section where there is house after house built on stilts and sitting out in the edge of the lake. I was fascinated by them. Presumably they are fishing camps or vacation homes, but I don't think I've seen anything like them anywhere else in the U.S. Some are somewhat elaborate, some aren't; some are kept up very well; some are in danger of collapsing. Seemed to me to be a phenomenon peculiar to that region.
Of course, if you're running late, you might pass these after dusk or later.
In New Orleans, I do recall that the track wraps around the Super Dome shortly before reaching the station.
You mentioned getting off the train to snap pictures, and you or someone else commented on "nice" or "not nice" stations. One thing you might be interested in is the series of pictures posted at
http://snow.prohosting.com/usarail. This site is devoted to posting, in highly organized fashion, pictures of all stations on the Amtrak system. They aren't all there, but it appears that you can start at Philadelphia at
http://snow.prohosting.com/usarail/philadelphia.htm (or actually just north of there) and see, in order, pictures of every station all the way to New Orleans. You can use those as a guide to see if there are any in particular you want to watch for.
Finally, having traveled via train with my own relatively small children (including a trip to Chicago back in the fall, on which they were 2.5, 5.5 and 7), here's a few thoughts on THAT. First, we make sure that we have LOTS of things for them to do--coloring, small games, books to read or be read to, whatever. Evidence of how well that works is that despite spending an extra 8 hours (10:00 am to 6:00 pm) on the train due to delays, everyone arrived cheerful! Also, make sure to take advantage of your ability to roam--think about having an early dinner (although as first class passengers, I'm not sure that I'd be THAT worried about the dining car being crowded, other than if there IS a delay, that might not sit well with the 2.5 year old!) and then come back later for dessert--just before bed, perhaps. Your attendant may be able to give you a heads up as to when to go. You can (and should) also go down to the lounge car--pay for a snack or two (blah food and expensive, but if it makes the kid(s) happy, do it anyway!), but even if you don't eat anything, just sit down at one of the tables for a change in surroundings. The kids get antsy, and sometimes just moving around helps. Walk to the back of the train to burn some energy. And pull one of the upper beds down to play on during the day--it's got its own window up there and the kids love being able to climb up there.
It's too bad you won't be in the deluxe room--if you were already willing to pay for it ($$$!), the extra space in there is nice, and the lower bed is as wide as a regular twin-sized bed (we take advantage of that by sleeping two--my wife and our youngest--in that bed and the rest of us each have our own bed). But you'll be fine with the two standards.
Enough miscellaneous rambling. Post back if there's anything else I might be able to take a crack at!
Have a great trip!
and he went off about how they had taken the train from Philadelphia, etc, etc, etc. and it was SO SLOW! I asked him why he had taken the train, because the times are well-published, and he said he took it because his wife wanted to. I felt sorry for her, as his boorish behavior was obviously not adding to her enjoyment - in fact, it was kind of a drag for all of us in his proximity. Because of some track work by Sacramento, we ended up 2 hours late into Emeryville. Not a huge deal, but I'm sure he was over the edge by then.