Hi Lisa,
I think there is no better place to celebrate a birthday than Disney World. We have been celebrating our boys' birthdays there for years and this year is even better as Disney is offering the birthday guest free admission to one park on his/her birthday. Be sure to register
here prior to your departure.
There are so many great things for your family to enjoy while at Disney World. You only mentioned a visit to Magic Kingdom, so I am not sure if you will be visiting the other parks, but Magic Kingdom is a great place to start. This park features the largest selection of attractions of any of the four parks. If your boys enjoy thrill rides, be sure to check out Big Thunder Mountain Railroad and Splash Mountain. Other classics that you will want to visit are Jungle Cruise, Pirates of the Caribbean, and Haunted Mansion. You will be visiting after the re-opening of the Hall of Presidents which will feature the addition of our newest President. this is a great stop to enjoy an escape from the heat and crowds as well as experience a fantastic look into our country's leaders.
You may want to consider enjoying a tour together. While some of the tours do not allow guests under the age of sixteen, you will still find a great selection
here. One of my favorites is Mickey's Magical Milestones which is a look into the creation and life of one of the most well know faces in the world. Tours can be booked ninety days in advance by calling 407-WDW-Tour.
This is just a small selection of what your family can enjoy at Magic Kingdom, A great idea, is to let each family member select two or three things that they want to do or see at the park and start there.
Wishing you a magical birthday celebration!