I agree most of the examples mentioned in the article fall under the umbrella of other kinds of abuse. When the author talks about the three roots of abnormality his patients describe

1) to eliminate or destroy children, 2) to make them play roles no child should play or 3) to dominate them totally, narcissistically erasing their identities.

These all just seem like forms of child abuse, presumably perpetrated by the caretaker, rather than a widespread prejudice against children.

From google:

Racism: The belief that all members of each race possess characteristics or abilities specific to that race, esp. so as to distinguish it as inferior or superior to another race or races

It doesn't sound much like "child" could be exchanged with "race" here. The idea is more like children are mistreated because they are helpless not because of a belief about some inherent characteristic of being a child.