Hi Janet!
Welcome to the Disney Parks Moms Panel! My son turned three a few weeks ago, and if there is one thing that I've learned from taking a toddler to Walt Disney World Resort many times is that all predictabilities that I know of him from being his mother for the last 1000+ days go right out the window the moment we cross under the most magical Welcome Sign.
What I can share from all of our misadventures is that
Disney Dining Locations are usually very, very accommodating when it comes to
adorable Mouseketeers. While you should definitely double check with a Disney Dining Cast Member, either by calling (407) 939-1947 or stopping by
Tony's Town Square Restaurant when you first enter Magic Kingdom Park, since your plan is to keep your dining reservation but switch from the
Festival of Fantasy Parade Dining Package to a regular Table-Service meal, this shouldn't be a problem.
If this is a plan for later on in your Walt Disney World Resort Vacation, I would pay attention to how tired your babe becomes during your first few Disney Days and when. I'd then use that information to judge if you should full-out cancel the entire reservation for everyone, which can be done up until 24 hours before your scheduled meal time. Or, if need be due to a meltdown or because your Disney baby fell asleep just before the dining reservation, as long as one person still dines under the original or modified reservation, the rest of the party can cancel day-of without penalty.
I hope this helped, Janet, and We'll See You Real Soon!
~Kristen