Hi there, Chris!
That's a great question, and one that deserves some consideration.
I've gone to
Walt Disney World with two little ones, and have used, at various times, a tandem double stroller (affectionately nicknamed "The Bus"), and a side-by-side.
Each of these options has advantages: space, first of all, and storage. A place for packages, and drink holders for the grownups.
But each one of these also has a significant drawback: maneuverability. When the pedestrian paths are crowded, navigating a wide stroller through crowds of people can become quite a challenge. And while doorways are completely ADA-compliant, sometimes wedging a double stroller through a door and around a stocked store can become quite an obstacle course.
One other issue to consider is that os independence. If your three-year-old wants to stay, but the baby needs a nap, do you send the entire double stroller with the baby, leaving the three-year-old with no travel option? The two single strollers, I think, afford a measure of freedom for each
parent that the double simply cannot.
Oh - and if you ruin one small umbrella stroller with spills, it's a lot less of an investment than some of the larger, more feature-rich doubles. Some people even purchase two inexpensive doubles in advance of the trip and leave them - or donate them - before the trip home.
While an initial instinct is to say "bring the double for ease of use,"
the two considerations of maneuverability and "splitting up-ability"
might help you determine a different course of action.
Have a wonderful trip!
See you later, celebrator,
-Deborah B.