No worries. There are many. many guests that need to be up and out early in the morning for early character breakfasts, early tours, or early BBB makeovers. Fellow Panelist Bret has some great information on the early morning transportation situation at Walt Disney World. I'm going to refer you to his post here.
Once you get to the park, it is VERY easy to get inside for an early character meal. You'll go through the security checkpoint and then you'll see a big row of turnstiles. There will be one turnstile marked with a sign that says something to the effect of "early character meal entry." Usually the entrance is at the far end of the row of turnstiles. If you don't see it right away, just ask any cast member. When you approach this early character meal entry turnstile, there will be a cast member there with a clipboard. They will double check that you have a reservation. They look it up by your name, but have your confirmation number with you too, just in case. Then you'll be allowed to enter the park with no problem.
Having a pre-park-opening reservation at the Magic Kingdom is one of my absolute favorite ways to start a Disney day. Because you are in the park early, you have one of the only opportunities available to get photos of your family in front of the castle without a zillion other guests in the background. Be sure to have your camera ready as walk down Main Street for your reservation.
Have a great visit to Walt Disney World.