Hi Lauren,
The parks themselves are quite large which is what makes WDW a great vacation destination. There is a lot to do at is Walt Disney World.
Traveling between the parks usually takes anywhere from 15-25 minutes depending on where you want to go. The provided transportation is very convenient. You can travel from the Magic Kingdom to Epcot using the monorail system. You do have to transfer trains at the Ticket and Transportation Center, but it is very easy and usually only takes 10-15 minutes.
You can travel between Disney’s Hollywood Studios and Epcot by bus, boat, or the walking trail. All three ways takes about 15-20 minutes.
When traveling to or from Disney’s Animal Kingdom you will need to use a WDW provided bus. Depending on which of the parks you are traveling between you can expect it to take 15-20 minutes.
When trying to estimate travel times, keep it mind that buses arrive at stops about every 15 minutes. You need to add that to the overall travel time.
Hope that helps
Michelle