The kid who was left in coach without visitation probably is an example of behavior that occurs on a daily basis in that family. I don't consider it neglect in this case, but it's not ideal behavior.
The situation where the kid is crying and the parents either think it's cute or do nothing to calm the child is neglect to the child and aggression against all others on the plane who are trying to sleep on the redeye. I consider this type of behavior as air rage by default. The kid has it and the parents promote it. The trouble with confronting the parents or weeking assistance from the FA is that they will scold you!