Ummm...I wouldn't let a kid in front of me because they are "younger," I'd let them in front because they are short.

And yes, if I noticed I was blocking the view of a short adult I would try to help out there too.
My DD loved the parades when we took her last year, in fact they have ruined all the local parades for her because nothing else is up to snuff. But we would never have been able to sit with her for an hour to wait for them. She would have made us and everyone around us miserable. Now before anyone jumps down my throat, no, I did not shove my DD in front of people who had waited. We found places where we could see despite the crowds and DH would lift DD up to see. It was fine, she was perfectly happy. But as the parent of small children, while I totally respect the right of older children, childfree people, etc. etc. to enjoy their vacations, in many ways they are the ones making it impossible to get a good seat for the parade UNLESS you are willing to sit around for an hour. It's kind of like people who line up to get onto an airplane with assigned seats before the flight attendant even begins boarding

Many of us with little kids can't do it, or else, if we did, you would come here and find posts about how there was this family waiting for a parade and their 3 year old was whining and complaining and running all around for an hour and why didn't those parents just take that kid back to the hotel, didn't they realize what a pain the kid was being/how "tired" they were, whatever.
I don't have a solution, I just wish people didn't assume that parents with small kids arriving "late" (and by some people's definition, late would be anything under an hour) for a parade are rude, pushy, entitled, whatever. Maybe they were just trying to be good parent and understanding their children's limits.
BTW, again, I stress, I am NOT excusing parents who push their kids ahead of people who have been waiting.
And re the lawsuit issue...it doesn't mean they would win, but that wouldn't stop some people from naming you in a suit. You can sue anyone about anything.