Hi, Christina! With young children,
Magic Kingdom would be your best choice. There are so many kid-friendly attractions, characters, and restaurants. There will plenty to fill your entire day, so arrive early!
There is a lot of walking, so plan to either bring a stroller or rent one when you arrive. You will get much more out of your day if your kids can rest their little legs!
If you want to do character dining, I suggest booking a meal at the
Crystal Palace (located right inside the Magic Kingdom.) Here, you can dine with Pooh and his friends at breakfast, lunch or dinner. Dining reservations can be made up to 90 days in advance by calling (407)WDW-DINE.
Have a great time at the wedding and also enjoy your day in Disney!