When Parents Play Favorites, All Children Pay the Price

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The Uncomfortable Truth About Favoritism

Most parents insist they treat their children equally. Research suggests otherwise — and the consequences may be more serious than many families realize.

A new study published in the peer-reviewed journal Development and Psychopathology examined 632 pairs of identical and fraternal twins, averaging around 7.6 years of age. The goal was to understand how differences in parental treatment affect children's mental health. What researchers found challenges some of the most common assumptions parents hold about favoritism.

The child receiving less attention or harsher discipline was not the only one at risk. Both siblings showed measurable mental health effects.

What the Study Actually Measured

Researchers chose twins deliberately. Because identical twins share nearly all their DNA and grow up in the same household, comparing them allows scientists to isolate the impact of environmental factors — such as how a parent behaves differently toward each child — rather than genetic ones.

Parents and children completed questionnaires and participated in home observations. Researchers measured differences in four key areas: discipline, intrusiveness (how much a parent interferes or controls), warmth, and outright favoritism. Children's mental health was then assessed across three dimensions: ADHD symptoms, internalizing behaviors (such as anxiety and depression), and externalizing behaviors (such as aggression, defiance, and rule-breaking).

The results were consistent and striking. Even modest differences in how siblings were disciplined or treated were linked to higher rates of anxiety, behavioral problems, and ADHD symptoms.

The Favored Child Is Not Safe Either

Perhaps the most counterintuitive finding: being the favored child offered no mental health protection.

Children who consistently received preferential treatment showed elevated levels of externalizing behaviors — aggression, defiance, and rule-breaking. Researchers suggest this may reflect a developing sense of entitlement when a child learns that normal rules and consequences do not apply to them equally.

"It turns out that siblings were very sensitive to differences in parental discipline," said Dr. Kathryn Lemery-Chalfant, professor of psychology at Arizona State University and co-author of the study.

In short, favoritism distorts the emotional environment for all children in the home — not just the one on the losing end.

Mothers and Fathers Shape Children Differently

One of the study's more nuanced findings concerns the distinct roles played by mothers and fathers.

Differences in a mother's discipline were more closely tied to internalizing symptoms — anxiety and depression — as well as ADHD. This may reflect the fact that mothers typically manage more of the daily discipline and spend more time with younger children. When maternal treatment was unequal, children appeared to internalize the imbalance emotionally.

Fathers' discipline showed a different pattern: unequal treatment was more often linked to externalizing behaviors. Children appeared to respond to perceived unfairness from fathers with outward acts of rebellion — rule-breaking, defiance, or aggression.

Favoritism also played out differently depending on which parent showed it. When mothers favored one child, that child tended to show more externalizing behavior. When fathers showed favoritism, the effects leaned toward anxiety, depression, and ADHD symptoms.

The researchers suggest that paternal affection may carry particular emotional weight for children, precisely because it is less expected or assumed. Unequal attention from a father, the data implies, can cut deeper than many parents realize.

A Two-Way Dynamic

The study is careful not to cast parenting as a one-directional force. Children's own behavior also shapes how parents respond to them.

During home visits, researchers observed parents and children playing a card game specifically designed to produce moments of frustration and impulsivity. What they saw was revealing: intrusive or harsh parenting often occurred in response to a child's inattentive or impulsive behavior — not the other way around.

"The parents were not causing children's negative behavior — they were just responding to it in a negative way," said Lemery-Chalfant.

Over time, this creates a feedback loop. A child with more challenging behavior may consistently receive harsher discipline. That child begins to perceive themselves as less loved or less capable. The parent, in turn, may grow exhausted or feel inadequate — and the gap in treatment between siblings widens.

Broader family stressors — financial pressure, emotional fatigue, inconsistency in routines — can amplify these patterns further. In some cases, parents with their own ADHD-related traits may find it particularly difficult to respond consistently across children.

What Parents Can Do

The goal, according to the researchers, is not robotic equality. Some children genuinely need more support at certain times, and siblings are often able to understand this when it is explained honestly and age-appropriately.

What matters most is consistency — particularly in discipline. Dr. Lemery-Chalfant recommends what developmental psychologists call an authoritative parenting style: one that combines genuine warmth with clear structure.

Practical starting points she recommends:

• Plan responses before problems occur. Knowing how you will respond to rule-breaking in advance helps parents stay calm and consistent in the moment.
• Use natural consequences. Consequences that follow logically from behavior — rather than arbitrary punishments — are easier for children to accept and less likely to feel unfair.
• Apply household rules consistently across all children. The rules themselves may be the same; the application should be too.

Age matters as well. Young children need immediate, simple consequences. Children in middle childhood are particularly sensitive to fairness and quick to compare themselves to siblings — this is when unequal treatment tends to have the sharpest impact. Adolescents, by contrast, are better equipped to understand that different treatment can reflect different individual needs.

The Bottom Line

What children need is not perfect, mathematical equality. They need to feel — individually and consistently — that the warmth and the rules apply to them. When that confidence is shaken, even subtly, the effects can ripple through their emotional development in ways that last far beyond childhood.

The research is clear: favoritism is not a harmless parenting quirk. It is a measurable risk factor — for every child in the home.

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Sources:

1. Lemery-Chalfant, K. et al. – Development and Psychopathology, Cambridge University Press: https://www.cambridge.org/core/journals/development-and-psychopathology
2. Arizona State University – Faculty Profile, Kathryn Lemery-Chalfant: https://isearch.asu.edu/profile/163574
3. American Psychological Association – Parenting Styles and Child Development: https://www.apa.org/topics/parenting
4. National Institutes of Health / NIMH – Child and Adolescent Mental Health Research: https://www.nimh.nih.gov/health/topics/child-and-adolescent-mental-health
5. Steinberg, L. – Authoritative Parenting and Adolescent Adjustment, University of Pennsylvania research overview: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3020292/

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