Hi Kassie!
If I had an extra day I would probably spend it in Epcot, I love touring World Showcase.Touring Epcot is generally better over two days so you have time to slow down and take everything in at World Showcase.Epcot is usually better suited for older children, since your traveling with a 4 and 5 year old I would suggest Hollywood Studios.
Hollywood Studios offers attractions and entertainment that are better suited for younger audiences. Shows like Disney Junior Live on Stage and Voyage of the Little Mermaid makes this a great place for entertaining younger audiences. It will also give you a second chance to see Disney's Fantasmic!, which is spectacular and my favorite show at Walt Disney World.Hollywood Studios is also home to
Jedi Training Academy,if you have a Star Wars fan that is between the ages of 4 and 12 this is a must do! Sign ups are done first thing in the morning and will usually fill up rather quickly, so two days in the park will give you extra chances to train your little Padawans.
Hollywood Studios is a park that really doesn't take all day to tour, so once you have hit all of your favorites I suggest taking a look outside of the parks.One of my family's favorite activities is the
Chip 'n' Dale Campfire Sing-a-long held at Ft. Wilderness.Two campfires are set up so guests can roast marshmallows or hot dogs where everyone's favorite duo Chip 'n' Dale are in attendance.A sing-a-long followed by a Disney Movie show are done nightly (weather permitting).Disney's resorts offer different activities and you do not have to be a guest to participate,I suggest taking a look at what each resort has to offer!I hope this helps and please visit us again if you have anymore questions!
Happy Planning!
Mandy