Aloha Sabrina! How lucky that you were able to get the dining plan for free during your Disney trip!
The Polynesian Resort has some wonderful views of the Magic Kingdom. Although the Hawaii longhouse has fantastic Magic Kingdom views and is close to the main building, it contains only club-level rooms. If you reserved club-level, you'll be in this building, but since you didn't mention staying club-level in your question, I'm assuming you're not. Between the Tahiti and the Tuvalu longhouses, I think you'll have the best views of the Magic Kingdom from Tahiti. The rooms in the Tahiti longhouse are also slightly larger than those in Tuvalu, and the bathrooms all have double sinks, which makes it easier for a family to get ready in the morning. The downside of Tahiti is that it's the farthest from the main building, the Grand Ceremonial House. However, it is very close to the Transportation and Ticket Center, so you can take the monorail from there instead of walking to the main building to catch it. An added bonus of catching the monorail from the Transportation and Ticket Center is that you can take a monorail to Epcot, as well as the Magic Kingdom; you don't have that option from the main building.
You'll definitely be able to see the torch-lighting ceremony at the Polynesian now, Sabrina! Hope you have a magical vacation!