Hi Erika,
You are going to the perfect place to make special memories, that's for sure. My ultimate choice would be
Narcoossee's which is located at the Grand Floridian Resort (I absolutely love everything about this restaurant), the service, the location (located right on the water front of the Seven Seas Lagoon overlooking Magic Kingdom), the food (such a wide variety from seafood choices to filet mignon, etc... and the best ever desserts) and of course the atmosphere. They do have a patio outside to watch the fireworks from or you can request a window table (the servers will even stop serving your dinner or dessert so you can watch the fireworks and not have your food get cold, etc...). Even if you don't get a window table, this restaurant is an airy, eight-sided pavilion with the seating facing the water and seeing the fireworks from any seat in this restaurant is easy to do.
There is no guarantee that there will be no children at Narcoossee's as it is only at
Victoria & Albert's that they have the "no children under the age of 10" policy, but because it is a signature dining experience, you will more than likely not see too many (if any) children at all. I hope this helps and that you can experience a most magical evening "just the 2 of you".
Best wishes,
Brigitta