Not all mothers are as wonderful as mine was, but I doubt that there is a need for a word
I; found in my dictionary "Momism" - blaming mothers for tje inadequacy of some children.
It may be true that many firstborne children get excessive discipline, and their siblings get
less because the mother hasn't as much time to dominate them. My sife compplained of that.

momism
n.
5coined (1942) by P. Wylie, U.S. writer < MOM & 3ISM6excessive, esp. sentimentalized, devotion to mothers or motherhood, thought to result in a mother‘s domination over her children and their failure to mature psychologically