After reading some of the posts, I feel in need to explain a little more in detail.
I have no problem letting a child sit on the curb in front of us if we are not sitting there ourselves. Since they are obviously shorter, they would have a harder time seeing. I am not a pushover about letting the adults push in front though.
I guess that is why I have a hard time understanding why they could not let our daughter sit in front of them (They had no problem letting their back pack sit there taking up extra space).
As for why we got there late, it was actually our fault. While I took DD's for a potty break, DH decided to leave the stroller parked in our space and asked the people sitting next to us to watch it so he could go grab the DD's a drink. He never thought someone would move it and take our space. When he got back the person he asked to watch it just shrugged their shoulders.
We always get a space about a hour before, even though DH thinks it is ridiculous.
I think it is sad the way people react to spots for the parade, and how mean they can get in front of children.

I would never ask someone to actually move for us or our child, but what about letting a child sit where there is room??? It is after all more for the children isn't it?
I guess I am in the minority on this, but if you ever need a spot to let your child sit, I would still do it in a heartbeat.