Illiteracy is child abuse like malnutrition is child abuse. It affects the child for the rest of its life and reflects poorly on the parents and the society that allowed it to happen.
I see illiteracy and malnutrition as no threats to the immediate physical well-being of the child, and therefore not child abuse if child abuse is to mean "that which justifies state intervention".
Teaching that government has a proper role in compelling attendance anywhere, except to court or jail, presents severe long term threats to children, parents, and society.
I see it as a far greater threat than illiteracy.