We took our kids on trips when they were around your granddaughter’s age (my oldest was 4 for his first trip and my youngest was 2 for her first one. They are 4 years apart). Like the others said, flexibility is key. Plan….but give yourself room to pivot when necessary. There will probably be times when it will be necessary.
You will probably want a stroller even if she doesn’t typically use one anymore. Whether that means bringing one from home (make sure it’s easy to fold) or renting one in the parks, little legs get tired fast.
Be okay with starting your day later and splitting the group if needed. There were days on my youngest’s first trip that my husband and I worked a divide and conquer strategy. One of us would get up early and go do things with our oldest that he wanted to do and the other would hang back at the room with the youngest if she needed more sleep. Or if she needed a real nap, one of us would take her back to the hotel while the other stayed in the parks with the oldest. Once she was up, we’d catch a bus to whichever park they were at.
Hit a bathroom before you get in line for ANYTHING that isn’t a 5-15 minute wait. We’ve had to work our way out of line a few times because a little one wasn’t going to make it until we got off the ride. Pull-ups or a change of clothes in your park bag aren’t a bad idea either—sometimes the nearest bathroom is just too far away.
Instacart some of her favorite food to your hotel—we used to get fruit, cereal, a small thing of milk, bottled water, some of our kids favorite quick snacks, bread, and lunchmeat delivered to keep in our mini fridge. Having a breakfast we knew they’d eat before leaving for the day, having fast access to snacks we knew they liked, or being able to make a quick sandwich after a park day often meant the difference between a hangry kid and a happy kid.
This is my biggest tip—treat it as a leisurely trip and not a “we have to squeeze everything in” trip. Being present and in the moment with your little for things you would normally blow right past on your way to the next ride or reservation will wind up being some of your most magical memories as they grow up. My oldest was OBSESSED with the Fountain of Nations at Epcot on his first trip—he would dance around or just watch the water for as long as we’d let him. We spent a lot of time in front of that fountain (we still refer to it as his fountain when we see pictures/videos). Then I blinked…. And now the fountain is long gone and he’s getting ready to start high school in the fall. On our trip last summer, I was legitimately in tears every time we were in The Seas because I would look at my kids and could still see the little versions of them that were amazed by all the animals. Both of those seemed like such little unremarkable things then…but they’re memories I will treasure for the rest of my life now.
Have so much fun!