I have never taken the boat from WL to MK. But, I have taken the boats from POR to Downtown Disney many times. I would say it depends on the Boat Captain (driver). I have never had a problem with leaving my double stroller open with my kids in it. They usually have me park it up next to the Captain in the front of the boat and ask me to put the wheel locks on. One time I was told by a particular Captain to fold it up. I asked him why, and he said that the strollers always have to be folded up on the boat. The boat was not crowded and I travel with 4 toddlers. Like I said, I have taken the boats many times and this particular Captain was the only one that ever had me fold the stroller up. Since then, I wait for the next boat to come if he pulls up to the dock. Not having to fold up the stroller was one of the reasons I preferred the boats to the bus. Also, at the end of the night my kids would always fall asleep on the boat ride back to the hotel. Hope this helps.