Hi Amanda,
There are very few requirements for what to wear while touring the theme parks. You can find the official rules on the
Walt Disney World Theme Park FAQ page.
As you can imagine, Florida can be hot and humid. Guests traveling during the summer typically wear shorts or capris, t-shirts, tank tops, or possibly casual sundresses. You should take care to wear comfortable, broken-in shoes. Even the most sedate Disney tourist will walk a minimum of 5-7 miles per day (often more). Be sure that your footwear is up to the task.
During summer visits to WDW, I usually will bring a light cardigan with me because I find the restaurant air conditioning to be quite chilly, but that's a personal preference.
Guests visiting Disney in the winter months usually wear jeans, sweatshirts and similar attire.
There are few restaurants at Walt Disney World that have a bit more of an upscale dress code. These are all signature dining venues located in the resorts, not in the parks. There is no specific dress code for Akershus. You can feel free to wear whatever you're wearing to tour the park that day. You will find that many young girls do put on a dress-up princess gown for the occasion, but not all do, and this is certainly not a requirement. My own three daughters have been to Akershus many times and have never chosen to wear a princess dress there.
Good luck with your planning. Please let us know if you have additional questions.