I like both Blue Bayou and Cafe Orleans and found that while they have a similar feel in their overall cuisine, they do have different menu items and an overall different atmosphere. Blue Bayou has all indoor seating and is located in the PotC building. Some of the tables (those nearest to the water) can watch the PotC boats float by (as they head through the bayou portion of the attraction). The restaurant is dimly lit (supposed to re-create the feeling of evening on the bayou). I've had pretty good luck with the items I've ordered and with the service. The prices are on the high side.
Cafe Orleans has a mixture of indoor and outdoor seating (most is located outdoors). It's a great spot to do some people watching if you have a table near the railing. With a lot of the seating being located outdoors, it's subject to the weather (so hot if it's hot or cold if it's cold). I've also had pretty good luck with the menu items I've ordered (I really like the pomme frites and gumbo) and the service. The prices are a bit lower than Blue Bayou.
If your main interest is in the Monte Cristo sandwich, then most folks recommend going to Cafe Orleans because the price is lower for the essentially the same thing (although, CO has two types and serves it all day long - there is only one type at Blue Bayou and it's only on the lunch menu). If that's not your main focus, then I would look at the menus and see which one interests your family more.