Seems to me a situation evolved around the OP, it doesn't appear to me that photographing unruly kids who were jumping on a park bench whilst elderly strangers share the same bench is a violation of their privacy. In my book, those kids were violating the privacy of those elders who were there first. I bet had one of those kids injured those elders Ming's pictures and corroboration of events would have helped. The actions of the mother I've no comment on....
So Ming, yes or no question, were there elderly strangers on a park bench that some kids (accompanied by their mother) turned into their play land?
Or were they all together - grandparents, uncles/friends, whatnot and their "energy intrigued you" and you attempted to photograph it?