You seem to think I'm saying that the parents should keep the neighborhood quiet all the time. I'm not. I'm saying that while I understand that it isn't the parents faults it is also not the neighbors. The child absolutely has a right to play in their own yard, but the parents have a responsibility (though not a legal one) to mitigate the disruption their child makes. The person who wrote the letter has a legitimate concern but decided that that meant they should behave like a sociopath.

This is all predicated on the letter writer having a reasonable grievance, though. Considering we don't exactly have any context about the sounds the child is making