To see if this was true outside of a study environment, Shute interviewed youngsters throughout her neighborhood in Maryland, many of whom said they felt their parent favored their siblings over them.
“It's either my older brother, who actually does things correctly, though he might mess up here or there, or me, because I'm awesome,” said David Lewis, a 10-year-old from the Bethesda, Maryland, area who has an older brother and sister.
Why does this happen? For mothers, it could be because of shared values and gender similarity.
According to a Purdue University study, mothers were more likely to favor their daughters, “which is not surprising because the mother-daughter connection has been shown in previous research to typically be the strongest, closest and most supportive parent-child relationship.”
The study, published in the Journal of Marriage and Family, said shared values about life between the child and mother led to the mother favoring that child over another. That's because the mother could depend on that child to make caregiving decisions for her or others in the family in the future.
The study, which collected data from 406 mothers, ages 65 to 76, over a seven-year period, did not look at how fathers favor one child over another. But another study from Purdue University said dad’s favoritism is important for children because it can create tension among them.
The study looked at 137 adult families where both parents were still alive, and found that children, especially daughters, reported tension between siblings when dad showed favoritism for one sibling over another.
“Fathers are important figures in families, and the father-child relationship is sometimes more tenuous than the mother-child tie,” Jill Suitor, one of the study's researchers, said. “Mothers are often more open and affectionate with their children, whereas fathers have sometimes been found to be more critical, leading offspring to be more concerned when fathers favor some children over others.”
There are some potential issues that creep up when children find out or believe that their parent has a favorite, Shute wrote for NPR. Alex Jensen, a psychologist from BYU, told NPR that “it's not just how you're treating them; it's how they perceive it.”
Perception that a parent favors one child over another often makes children misbehave, according to a 2014 study published in the Journal of Family Psychology.
The study compared a parent’s differential treatment to the adolescent’s delinquency by analyzing 282 adolescent sibling pairs. The study found that when children perceive that their parent favors their sibling, they are more likely to drink alcohol, smoke cigarettes and take drugs, according to the study.
“It’s not just how you treat them differently, but how your kids perceive it,” Jensen said in a news release. “Even in the case where the parents treated them differently, those actual differences weren’t linked to substance use — it was the perception.”
Favoritism by a parent can affect more just a child. It can affect the whole family, too, according to a 2013 study published in the journal Child Development.
The study, which analyzed 400 Canadian families with children ages 2 to 5 years old, found that children are more likely to suffer mental health problems, “such as aggression, attention and emotional problems,” when each child in the family is parented differently.
So what can parents do to help their children understand there isn’t a favorite?
“Show your love to your kids at a greater extent than you currently are,” Jensen said. “As simple as it sounds, more warmth and less conflict is probably the best answer.”