You have described a number of situations in this thread in which you have encountered these difficult children and their clueless parents.
Tell me, in your capacity as a childcare worker, what is your rationale for "tuning out" a tantrumming child? Is ignoring a child's misbehavior appropriate, or should you have attempted to redirect him? What message does it send to other kids when you tune out one that is clearly distressed? Do you just explain to them that he is BAD and doesn't deserve pie??
I am not a big fan of irresponsible parents, but I think bad parenting is usually due to ignorance or having suffered poor parenting themselves. And I don't think every time a kid has a meltdown it is because their parents are horrible.
It strikes me that if you changed this story slightly and it was a DOG who was misbehaving in public, almost nobody on this board would think it was appropriate to be mean. Some would likely suggest that the police should be called on the owner, or that the dog should be taken away from her. Almost no one would say the dog was a brat.
That is because everyone understands that it is the master's fault when a dog misbehaves. Everyone understands that dogs behave the way they are trained to. Nobody thinks that not feeding the dog will teach it a lesson, or that it's master will learn through the dog's suffering. People would feel sorry for the dog. People would intervene on its behalf.
Children behave the way they are trained to behave. A child who is misbehaving due to parenting defects deserves compassion and support, not mean spirited object lessons.
Your own children are fortunate to have such a good parent. It is too bad that they are being taught to be judgmental and intolerant instead of kind. The world could really use more kind people.