Child harrassed by another partent?

[mikesmimo]

My nine year old son was involved in a physical playground fight with another classmate. The children were apparently unsupervised and teachers still unaware for the rest of the day. The parents showed up at my door. The father rang the doorbell, the mother in the car. The father asked for my husband and me, but we were still at work (my mother was home with my son). The father then asked for my cell number and at that point the mother gets out of the car, was visibly agitated and began interrogating my son over the incident without any other adults present. Did these parents have the right to do any of this? I am thinking that once my son said we were not home, they should have left without saying another word. What is the law on this matter? We live in NEPA.