Hi Ginaida!
Thank you for bringing your question to the Disney Parks Moms Panel!
I love an early morning breakfast at
Magic Kingdom Park. There is something so magical about being there as the day begins!
If the park opens at 9:00 a.m., they will generally let Guests begin to enter as early as 8:00 a.m. These Guests are only allowed to roam around on Main Street, U.S.A. until park opening, with some of the
Main Street shops open for them to browse. So, you shouldn't have any issues at all getting to your reservation. There is a special line dedicated to Guests who have dining reservations prior to park opening. If you get there before 9, I would head to that line to get in, as it should be shorter. If you don't see the sign for that line, simply ask a Cast Member to point you in the right direction.
I hope this helps. Please let me know if you have any other questions and have a magical vacation!