Pedofile perhaps. Adults conversing with children after the parent says to stop is harassment.There are a-holes everywhere. Try to control the things you can... for example, couldn't they have gotten up and moved to another table? If he followed them, they could then speak up and ask for help.
I certainly wouldn't write off the whole campground over one a-hole camping there. You yourself said you don't know how they could have handled it better.
As for those saying call law enforcement... for what? What laws were broken here? Unfortunately being an a-hole isn't against the law. Or maybe fortunately, since we all are once in awhile.
Disorderly conduct, public intox, causing fear and panic for young children.