Hi Blake,
If your children are up and at 'em and you can be at the Magic Kingdom by 7:00 a.m, then by all means, take in a couple of attractions and work up an appetite before heading off to breakfast.
The attractions usually open during extra magic hours are located in Fantasyland and Tomorrowland. With a 6 and 3 year old, you'll probably want to use that extra hour in Fantasyland, and I think you'll find that you'll be able to experience at least 2 (maybe 3) attractions during that time.
If Dumbo is something that your children need to ride in order for their Magic Kingdom experience to be complete, then head to this attraction first. Other attractions usually open in Fantasyland during this time are:
- The Many Adventures of Winnie the Pooh
- Peter Pan's Flight
- "It's a small world"
- Cinderella's Golden Carrousel
- Mickey's Philharmagic - although, I would probably wait until after breakfast for this attraction, simply because it's a 3D movie that may take a little more time to enjoy.
You'll want to arrive at your restaurant 15-20 minutes prior to your reservation, so that gives you about an hour to play before sitting down to a great character meal. Both restaurants are extremely popular, and Crystal Palace is one of my favorites.
Hope this helps. Have a magical vacation!