Welcome to the Moms Panel Jason! We're so glad you're hEAR!
Table service restaurants don't "hold" spots for guests without reservations. However, if there is availability they will do their best to accommodate guests without reservations.
If you know the date that you'll be visiting the parks, I'd recommend going ahead and
booking online or calling 407-WDW-DINE. If you don't know the exact day or are unable to get reservations, you can try walking up and checking availability. You may have better success if you check just as lunch or dinner is starting. That way you'll have a larger time frame to try to get in.
If your family consists of little ones who may be disappointed if they don't get it, I'd send an adult ahead to scout it out. Your chances may also increase if you are traveling during a non-peak season.
If you are unable to get into a table service location, don't worry. There are quick service dining locations at all of the theme parks and Downtown Disney. If you need suggestions, let us know which parks you'll be visiting and the ages of your travel party. We'll be happy to make some recommendations for you.
Wishing you minnie magical memories :-) Allison