Hi Catherine and welcome to the Disney Parks Moms Panel!
There never seem to be enough hours in the days at Walt Disney World Resort. I completely understand why you would want to make the most of your day at the theme parks. The short answer to your question is, it depends. If your single day
ticket is not a complimentary ticket or restricted ticket, you should be able to upgrade the ticket to the Park Hopper option. You simply need to visit any Guest Relations location at the parks or at Disney Springs and you will pay the difference between a one day, one park ticket and a one day ticket with the Park Hopper option.
If you decide to stay with the one day, one park ticket and find yourself with extra time, I recommend a meal at one of the beautiful Walt Disney World Resort Hotels or at Disney Springs. Some of my favorite restaurants at Walt Disney World Resort are at Disney Springs!
Catherine, thank you for visiting us with your question. I hope you'll let us know if we can help you with any other questions!
Wishing you happy planning,
Amy H.