You can mince words all you want, but laughing at the "humorous" sight of a child "crammed into a stroller", is laughing AT the child. You might not point and make fun, but you are laughing at them, and if they see you reacting that way they will feel bad about themselves. You can try to justify it all you want, but your stripes are showing.
And you can try and pretend all you want but if you walk thru a crowd with a child very obviously crammed into a baby stroller people are going to laugh. And if you don't think they are then explain the success of all the shows that are on TV showing things like this for a laugh, and a lot of comedy is based on exaggeration. Like the clown driving the itty bitty car. Ertle (sp) wearing the extremely short pants.
So if you don't want people laughing don't give them anything to laugh at, get the proper equipment so the child doesn't stand out. Don't put the child in the embarrassing position of trying to fit where they don't.
Another thing the majority of people asking these questions don't have special needs children, it is only on the Dis that every conversation has to get back to special needs or hidden disabilities.