Hi Danielle,
I, too, find some variations on the physical addresses of the theme parks when I search the most popular mapping sites. But here's the good news: If you get anywhere in the vicinity of the Walt Disney World resort, you should have no problems finding the theme park you are looking for. The highways are well-marked with the best exits for each park.
Once you are anywhere on Disney's vast property, the signage is frequent and very clear.
I find if I simply put the name of the theme park, Lake Buena Vista, FL into any of the mapping tools, I get the proper directions.
But just to ease your mind, here is the physical addresses that appears to work perfectly for Magic Kingdom: 3111 World Drive, Lake Buena Vista. You can use that for Epcot and Disney's Hollywood Studios as well because you pass the entrances for both parks on World Drive enroute to Magic Kingdom.
The address that worked best for me for Disney's Animal Kingdom in Mapquest is 551 N Rainforest Road
I hope that eases your stress about getting lost. Disney really does make it simple for guests to find their way around the property.
Please let me know if I can answer any other questions as you plan your trip. Enjoy!
Wilma