Hi Andrea!
Thanks for your question. What a great age for your daughters to be visiting
Disney World. They're still within the age range where everything feels magical, and the Disney characters have truly come to life! :-)
So the
stroller rentals at Disney World are incredibly durable, yet nimble enough to get around the
theme parks fairly easy. Double strollers are double the weight carry, which is 100 pounds or less as the official recommendation. So as long as your two girls don't exceed that total amount, it shouldn't be a concern.
I would highly consider getting the double stroller as opposed to a single stroller. If both children get tired at the same time, the stroller works out perfectly as there really is nowhere in the theme parks where they can lay down and take a nap. I've seen instances where parents would rent a single stroller, then have 1 child in the stroller seat while the other sits on top of the stroller seat cover. I strongly would not recommend that.
May you and your daughters have memories that will last a lifetime at Disney!