Hello Elizabeth,
Thanks for stopping by planDisney with your question. It looks like your magical vacation is coming up soon. You must be so excited!
The only way to visit two or more parks in one day is to add the
Park Hopper Option to your tickets. You won't be able to use two single day tickets to visit two different parks on the same day. However, you absolutely can visit a park, like Magic Kingdom, leave to take a break during the day and then come back to Magic Kingdom in the evening. You don't need a Park Hopper to be able to do that.
With the Park Hopper Option, you would be able to visit all 4 parks in one day if you were really ambitious. After 2 PM (or whenever park hopping begins for the day) you can go to any other park you like, and you can even come back to the park where you started.
I love the flexibility of having a Park Hopper, especially if we are staying at a resort close to EPCOT. You can start your day in one park, then hop to EPCOT to enjoy one of the many festivals. It looks like you'll be arriving just in time to catch
EPCOT International Festival of the Arts. There are a ton of food studios (food kiosks) with a variety of delicious foods to sample. You can dine around the World Showcase for a fun dinner, no reservations required.
Hope this helps. Have a magical vacation!
Diane