Just to clarify....
There are designated areas OUTSIDE of the entrance to the line itself (in most all cases) where you leave your stroller and you must then carry or have the child walk through the line to the ride itself. So it isn't like you're about to board and you just leave your stroller right there.
While there are usually CM's working the area around the stroller parking area - they don't 'watch' your strollers - they are just in charge of making sure the strollers are arranged in a way to fit all the necessary strollers. There can be 20, 40, 60 strollers in one area - so obviously, they don't know whose is whose and in theory - someone could take the wrong one intentionally or unintentionally. This USUALLY doesn't happen - but I just want to make sure you know so that you don't leave any valuables in it.