Boma will give you food choices from mac and cheese and spaghetti, pasta and meatballs and the ole' standby chicken nuggets to foods that you will not encounter in any other Disney restuarant - like coconut tiramisu, zebra domes, DELICIOUS soups, salads, humus, meats roasted on a spit, etc, etc. - not to mention the ambiance of the restuarant and the experience of the hotel. At a specific time each night, the hotel has someone dressed in the authentic African garb telling stories around a fire pit - the children might enjoy this before or after diner, (you may want to call the hotel itself and find out what time this happens so that you could plan your dinner around it) also you are free to view the animals from around the pool area, or from the decks off of the lobby. Boma give you an "experience" not just a diner.
By the way, Boma is our family's favorite restuarant in and out of WDW.
LeCellier - although it has great reviews here on the boards, - was not anything above ordinary and even disappointing - to my family at least.
Ohana is nice if you really like meat - the menu is a little heavy on the meat and light on the starch and veggies. But they do have diner activities for the kids, and if you plan dinner right, you could watch fireworks over MK after dinner on the Poly beach. Also its a set menu, so if your kids are picky its not the best choice.
Mama Melrose - Good enough resturant but don't feel you have to do Fantasmic package. You get really good seats about 1 hour ahead anyhow. The Fantasmic seats are off to the side if I remember correctly. And as the restuarant goes - Its nice, but you can have Italian food anwhere.
What ever you choose, enjoy!! Have a great vacation.
P.S. - You might want to keep your eye on the new restuarant which will be opening in AK Park - Yak and Yetti. As far as I know there are to open in the fall - but I don't know anything about their menu. I would make my PS's now and keep my eye out for reviews you could always change later.