The kid is 4. That's not "lack of respect towards the parent". That's the kid being 4. Do you have a kid?
And maybe this was a terrible parent. Or maybe this is the one time the kid escaped her watch and it just so happened to end in the worst possible way. I'm assuming you clearly know the answer to this, otherwise you wouldn't be jumping to such a conclusion.
Or, possibly, instances of this are so rare, that when they do happen maybe we chalk it up to unfortunate accidents and not instantly call for the head of the parents because you and a ton of other people managed to make it out of the Grand Canyon ok.
To be fair, a lot of people die at the grand canyon, Here's a 4 year old that fell: http://www.cbsnews.com/news/preschooler-killed-in-grand-canyon-fall/
Apparently, about 12 people per year die there "... an average of 12 people die there annually, according to park statistics." http://www.cbsnews.com/news/texas-man-falls-350-feet-to-his-death-at-grand-canyon/
Short of plexi-glassing the world out, there's always going to be someone who manages to find a way.