Hi, Erin, Glad to hear you will be coming to Walt Disney World!
While it does seem convenient to leave your items in your stroller, for items as important as your medications, I would not leave those behind. Even if your stroller did not get moved, accidents do happen and a guest might grab your stroller thinking it was theirs, and although I am sure is extremely rare, a bag could get stolen from your stroller. Please keep your medications and any other valuables with you!
Also, strollers will get shifted around! For safety reasons and to keep foot traffic moving smoothly throughout the parks, there are designated stroller parking areas, often in sunny locations. Rarely have I found my stroller where I left it, even if I parked it in a designated stroller area.
An option you might want to look into is storing your medications at a First Aid station (they are located in each of the theme parks and water parks.) For more information on traveling to Disney with Diabetes, go to
www.allears.net and search "disney with type 1 diabetes."
I hope this helps and I hope you have a great vacation!