Do mothers' parenting attitudes & behaviors change with their first- and second-born? New research reveals that mothers hold similar views and attitudes when parenting their first and second children, but their parenting behaviors with their two children differ. Source 4r.
I would be surprised if a study showed otherwise. The experience is going to be different with each child as the mother changes and develops, and the children they raise change them in turn.
The way this change manifests has spawned a long series of jokes over the years, usually depicting the first child being approached with a combination of anxiety, wonder and devotion, and later ones with practiced practicality.
I was night compared to my older brother being day when my mother was raising us boys. I can say that the parenting of all three of us was vastly different. I am glad when I was 18 and out of the house due to that parenting. So yes I would say mother's differ on how they treat and raise their children.