According to a study that surveyed 610 adults in North Carolina,13.4% of parents say they are alienated from a child.
If the trend works out to be valid for all of the United States, that works out to be 22 million alienated parents.
If each parent has two children on average, and if both children were alienated, that would work out to 44 million alienated children.
Half of the parents say the alienation is severe, so as many as 22 million Americans might have suffered from DSM 5 Child Psychological Abuse V995.51
Here is additional information about the ubiquity of the problem in Ontario Canada.
Based on Dr. Harman's study (see above), Central Ohio Parental Alienation estimates that about a million US Children are abused this way each year, according to the following assumptions and estimates:
13.4% of parents report being alienated from at least 1 child (see the study above)
At least 13.4% of children are alienated (though it is likely higher because of parents with more than one alienated child.
Half are reported to be severe 6% (see the study above)
Parents assumed to have to be 18 or older
Life expectancy 70, leaving 5/7th of parents are of age to have kids
321.4 million people in US
5/7 of 321 is 229 parents in the US
6% of 229 parents is 13 million alienated parents (and children)
At least 13 million children, across all ages
Active abuse for 13, 14, 15, 17, and 17 (5 years), though it often becomes more apparent at age 9
5/7 of 13 million kids is 928 thousand kids being abused each year
Most are being abused each of those years, though for some, divorce starts in middle of the range
Each year, a millions kids a year are being abused psychologically
This estimate also holds for most units of time that is significantly less than the 5 year range 13-17
Other worthwhile topics:
ABC 2020 Exposes Parental Alienation: Footprints in the Snow
The attachment model of parental alienation that uses only standard and accepted/established psychology