Hi and welcome!
I'm not sure I would count on free dining in December. It's one of their busiest times of year, so they have no need of any sort of promo to lure people into the parks.
Here's where I would start: take a look at the resorts at
www.allears.net Decide which of the resorts would be a good fit for your budget and your trip. Book it ASAP. WE LOVE the Deluxe Resorts, even though they're more expensive.
Decide whether or not you want the meal plan. We didn't get it last August, and to tell you the truth we really missed it. But it's not right for everyone, so you'll need to do your homework here.
Consider working with a Disney Certified
Travel Agent-- lots of us can recommend some pretty fabulous agents. It wll mean someone else to keep an eye out for potential discounts.
Something else that helps us a lot: Every single holiday and birthday in the year leading up to a trip means a Disney gift card...or 2 or 3. You'll be amazed at how quickly the spending money can add up that way.
We don't go in December, we go in August. (We're both teachers.) We manage to hit Value Season, so the room prices are discounted quite a bit. Plus we always manage to snag some sort of great room discount. If that's a possiblity for you, it works quite well for us!
http://www.mousesavers.com/historical-information-on-walt-disney-world-resort-discounts/#codechart has a list of the discounts that have been offered in the past.
Even though your kids aren't real young, do at least one Character meal... I suggest Chef Mickey's. We also LOVED the meals we had at Cape May (a 2 minute walk from Epcot, at the Beach Club, The Seafood buffet was wonderful!!!!), our lunch at Le Cellier, our lunch at Yak and Yetti (in Animal Kingdom).
Learn the ins and outs of Fastpass. If you're going in December, you can expect high crowds. Knowing how to use Fastpass will save you time and aggravation.
Also, we love our Photopass. We always pre-buy the CD at a discounted price, and have lots and lots of pictures that actually include my husband.
Plan to be at the parks at Rope Drop (opening) each day, with at least a minimal plan of what you want to do. For example, when we get to the Magic Kingdom, I go ahead of the family with all our tickets and Fastpass Peter Pan, then meet them at Thunder Mountain. We crank out Thunder and Splash Mountains, then use our Peter Pan fastpass. We don't stick to a strict touring plan, but we do a lot of that sort of stuff-- I'll run ahead for a fastpass, then meet them all someplace. In Epcot, I run and get us Soarin' fastpasses, then meet them at Soarin-- we do it twice in a row before the lines get out of control. We do the same thing at Hollywood Studios with Toy Story Mania-- last year I rode it with 2 kids while my husband did Tower of Terror with our daredevil, them he met us at Toy Story Mania to use the fastpasses. A little planning really goes a long way. Don't let your family be that one that spends hours on lines if a little planning can avoid it!
I'm guessing I've overwhelemed you, so I'll stop here. Have fun planning!