Parental Differential Treatment

Consciously or unconsciously, many parents have favorite children.

The implication of this is that they also have less-favorite children, and this favoritism—whether intentional or not, whether real or simply perceived by a given child—can in some cases impact both favored and non-favored children for the rest of their lives.

This dynamic, often called "parental differential treatment," can impact the bond between siblings, even into adulthood, and for a variety of reasons this topic is unlikely to ever be brought up by children or parents, which makes remedying the situation tricky.

All of which is problematic, because among other outcomes, people who are not the favorite (or believe they're not) have been shown to be more prone to some types of addiction, depression, and attention-demanding, risky behaviors.

It can impact a person's ability to form relationships with others, their capacity for empathy, their sense of rightness and fairness and value, and may sometimes negatively impact a young person's ability to healthfully transition from child to young adult.

Research suggests that impacts differ based on, among other variables, who's doing the favoritism (mother or father figure), how positively or negatively valanced the sibling bond is more generally, and things like sibling age-difference and the culture and context of the family in question.

Some of the relevant studies have been ultra-specific and thus not necessarily broadly applicable, while others have been long-term and fairly expansive in scope, gesturing at common family dynamics rather than fairly narrow cases.

The general consensus amongst experts seems to be that the solution to this issue is not to attempt to treat all of one's kids exactly the same way, but instead to adapt to who a child is as they grow and to be aware that it's possible to accidentally create an atmosphere of inequality, and to be conscious of the possibility that even small, perceived slights—over time—can develop into a complex that can be addressed, but only if the elephant in the room is acknowledged (which is pretty rare), accepted, and accounted for.