
as long as it is not locked
to anything, it will be OK.
But, you mentioned your son can't walk at all, so you really don't have to worry about his chair. For some attractions (like shows) he will be able to stay right in it from the time you enter the line until you are done with the attraction. For ones where he does need to get out to board a ride car, the wheelchair is usually going to be at the same place where you boarded the whole time. The CM might move it if it is in a pathway (like if you pulled it up very close to the ride car to board), but it will not be far from where you left it. People getting off have no idea who the chari belongs to or if they might be in the next ride car, so they leave them alone.
I would bet that most people don't even notice those wheelchairs at the exit. They are focused on getting out and most of the time don't even see it.
As for anyone sitting on your childs' feet, that happened a long time ago and we were pretty vocal for our DD. Recently, when we went to Lights, Motors, Action a man with an
ECV was just behind us in the line. He parked his ECV and his wife and small child sat on the ECV while he sat on the bench. The wife proceeded to prop her feet up on the tire of my DD's wheelchair. I was sitting behind DD and didn't say anything because DD had not noticed. I figured if she did and hauled off and hit the lady, it would serve her right. That lady (if you can call someone really rude a 'lady') ignored DD and turned her head the other way when DD tried to engage her by smiling (DD can't speak, but she understands just fine). The lady also cleaned underneath her fingernails and flicked the 'junk' over by DD's wheelchair. I was half hoping DD would hit her, but she didn't.