Study: Favoritism's Sinister Side

“It’s not fair!”

How many times a day do you hear that? Siblings whining about one or the other getting preferential treatment—be it a bigger slice of cake or  a cooler pair of kicks or a longer video game session—is simply a fact of life in most homes. If you hear it a lot, however, stop and listen. A new study just published in the journal Child Development has found that if parents consistently play favorites, all the kids in the family suffer.

When a parent gives primarily positive feedback to one child, and primarily negative feedback to another, it’s known in psychology circles as “differential parenting” and no one would be surprised to hear that the child who is the recipient of the negativity suffers. But this study, which followed 400 Canadian families with up to four children between the ages of 2 and 5, including in-home observation, found that the siblings who received the positive parental attention also had a higher incidence of problems with aggression, attention, and emotional issues.

Plus: 6 Ways To Stop Sibling Fighting

"Past studies have looked at the effects of differential parenting on the children who get more negative feedback, but our study focused on this as a dynamic operating at two levels of the family system: one that affects all children in the family as well as being specific to the child at the receiving end of the negativity," explains Jennifer M. Jenkins, Atkinson Chair of Early Child Development and Education at the University of Toronto, who led the team.

Mothers with a lot of risk factors—because they were single parents, had income worries, or experienced past abuse, for instance—were found to be more differential in how they treated their children than moms whose lives were less stressful. These moms had a wider range in the amount of warmth and affection they showed and how harsh and irritable they were with different children in the family.

Plus: When Parents Play Favorites

The main takeaway: When siblings in families are parented very differently, all children are at risk of developing mental health problems. "In all likelihood, this occurred because differential parenting sets up a dynamic that is very divisive," Jenkins notes.

Tell us: Do you ever catch yourself playing favorites?