Cheryl,
That is a great question!
I am a big fan of both
Tusker House and
Boma, so either way you go, you are going to have a great time. But let's make for the best possible day.
I would suggest that going to a sit down meal at lunch, any sit down meal, is taking key park time and spending it at a table instead of at an attraction. If you go with your plan to go to Boma for dinner, you not only help save more of your midday time for attractions, but you solve that long-standing problem of what to do on an Animal Kingdom day in the evening, when the park gets a bit sleepy. By going to the Animal Kingdom Lodge, and dinner at Boma, you get to experience one of the finest Walt Disney World resorts. And you do it in the evening hours when it is unlikely you would have gone back to the park anyway. As for the resort itself, the theming is exotic and the animal viewing areas are worth the visit.
BOTTOM LINE: Choosing dinner at Boma over lunch at Tusker House will extend the entertainment value of your overall day, free up valuable midday park time, and deliver a meal that is both exotic and adventurous (for the adults in the party), as well as safe and familiar (for those two picky girls)!
Have a magical (and delicious) vacation!