It depends on the harm that you witness. Your question does imply your awareness that parents are not/may not be intellectually (or even morally) competent.

In no Western society that I can name are parents omnipotent owners of their children. Parents may even lose custody of their children. If you know that parents are doing physical harm to children, you have a social obligation to try to do something for those children.

Even though we may turn a blind eye, we do have a social obligation to all children. Human anthropological history reflects this.

Although intellectual harm tends to be seen as sunken cost (and possibly "correctable"), social harm has intolerable consequences.

We should be involving our community members more in the exchange of ideas, and digital sources of information quite a bit less.