Okay, I'm throwing my hat in the ring here, as a non-parent. Yes, non-parent.
Unless it's clearly abbussive behavior, no one has the right to judge how a parent is or is not disciplining their child.
I have a younger brother (6.5 years) on the autism spectrum, and if you think your kids can throw tantrums, boy, you haven't seen anything until you've seen a twelve year old throwing a melt down that a three year old would have. Or a six year old charging away from his parents because he saw an elevator in a restricted area and decided he had to head for it. Yes, my parents often got angry with my brother. When I was responsible for him growing up, oh boy, could I lose my temper with him when he would charge away and I'd be running after him. We would often get strange looks in public, like, "Can't you make him behave?" It was adding insult to injury. Here you were, dealing with a child who wasn't behaving, and strangers were making it worse. If my parents were disciplining my brother, I often stood away from them to look like I wasn't with them. And then if I was responsible, then I was getting those looks, and it was my humiliation.
I decided a long time ago that I was not going to be that person who would stand there and judge parents for how they were disciplining their children, or if they put their child on a leash because they were a runner (believe me, I get it. More than once, my brother just walked clear out of the hotel room. That was fun). Instead, I smile at the parents, laugh a little, shrug it off, like, whelp, what can ya do? Let them know they're doing a good job. After all, I know I wasn't a perfect sister with my brother, I just did my best, so I can imagine it's the same with parents.