Hi Alison!
Thankfully, Disney has a wonderful complimentary transportation system that can get you where you need to go anywhere within the Walt Disney World Resort!
There are so many things to do and see outside the Parks, I almost don't know how to start!
First of all, September will still be warm enough for swimming, so pack the trunks and enjoy some pool time at the fabulous new Art of Animation Resort! The pools there are absolutely unbelievable!
If that's not enough water, consider the Disney Water Parks - Typhoon Lagoon & Blizzard Beach.
Also, try spending some time in the
Downtown Disney Area for shopping, dining, and entertainment, such as the Lego Store, the World of Disney, Al's Toy Barn, the 24 screen AMC movie theater, and DisneyQuest, an incredible indoor interactive entertainment complex. They are sure to really love dining at T-Rex or the Rainforest Cafe there.
If they are sports enthusiasts, spend some time at the
ESPN Wide World of Sports Complex. You can tour the complex, which is home to the Atlanta Braves for Spring Training. Check the calendar to see if there are any events or camps in which your boys can participate.
Also, be sure to visit the
Recreation page on the Disney website to find out more about arcades, playgrounds, Movies Under the Stars, Campfire Singalongs with Chip & Dale, Animal Programs, Kids Programs, water craft rentals, fishing, miniature golf, carriage rides and more!
I hope this helps get you started in your planning! Have a wonderful time!