Hi Christine ~
Ticket Options can be confusing and can change without notice. I called Disney to speak with a Cast Member so I could give you the most current information.
The Cast Member I spoke with said their system will not allow Guests to enter 2 different parks on the same day even if you use 2 separate single day tickets unless you purchase the Park Hopper Option. She said that when you purchase the tickets, they are linked to your name. When you enter a park, their system notes that entry along with the scan of your finger. If you try to enter a different park on the same day without the Park Hopper Option, their system will see that you've already entered a different park earlier that day and entry will not be allowed.
You will save yourself a little money by purchasing multi-day tickets as the ticket price per day goes down the more days you buy. You won't save a lot of money on a 2-day ticket, but every little bit helps. Here is some information that may explain
purchasing multi-day tickets a little more in depth.
With a 1-park per day ticket, you can visit 1-park per day. You can leave and re-enter that same park as many times as you'd like but you can only visit 1 park that day. The Park Hopper Option allows you to go between all 4 of the theme parks in 1 day if you'd like. The current cost (always subject to change without notice) to add the Park Hopper Option is a one time fee of $59.00 (+ tax) for 2 or more days. If you think you'll plan on visiting more than 1 park on at least 2 days of your trip, then the Park Hopper Option would probably be worth the extra money. If not, I'd try to focus on the park I was visiting for the day and save the money.
Wishing you minnie magical memories :-) Allison V.