Haven't Lost An Eye Yet!
I volunteer in a museum full of big airplanes where, if you're carrying a child on your shoulders and are not really careful, you can dent an airplane and leave bloody marks on foreheads. Throw in that the floor is a concrete slab at least a foot thick that is not getting any softer, and you have a recipe for disaster should a kid take a head dive.1. There is no one behind them
2. The fireworks are behind them which means they are not looking at the fireworks but staring aimlessly at Casey Jr.s
Yet gently reminding visitors of those two points usually elicits "Thanks. I'll be careful."
So it seems that not even pointing out the potential for injury to their child will dissuade them from this behaviour.
God forbid that Dad or Mom should trip on a curb or someone else's feet while their child is five feet or so above the pavement... in the dark... with loud, distracting noises and music going on around and over them...