Honestly, I find it SO MUCH MORE rude when parents feel the need to make such comments or throw glares at people they don't know simply because they're standing in a spot that in less than two minutes, they will be standing in themselves.
What is that teaching the children of these parents? It is teaching entitlement, and *gasp* rudeness, because apparently it is OK to talk and treat people like that, and the children can only sit and watch and soak it all in.
Honestly, when I was little and in Disney World, sure I was hot and tired, but you know what? I would still have been hot and tired no matter what, and I certainly didn't care who else was riding.
I was raised to be CONSIDERATE of others, and let them do what they like to do without passing judgment or prejudices. You DON'T KNOW those people, what their lives or like, or what ordeals they've had to face, or anything about them.
I give up my seat on the bus if an elderly, pregnant, or sick person gets on. I hold open doors for people, and will go out of my way to help someone I see struggling (dropping a bunch of boxes on the floor, etc.) but I will stand in line for Dumbo patiently, and do what I can to think of others in line, but I will do as my parents raised me to do and "mind my own beeswax".