> You normally put that in a stroller but that's a huge pain to manage on a bus or subway.
Not in any bus or subway car build in the last 20 years.
In every EU city I rode mass transit in the last decade, all transit vehicles are "low side wagons", meaning you can just roll on from the platform/curb, the doors are wide and the area right behind the door is a large space for wheel vehicles.
People bring wheelchairs, strollers, bikes, ect. without any problems, without needing help getting on. The platforms have elevators, for the people not comfortable taking a stroller onto an escalator.
The only exception I can think of are historic drams, but those are rare.