Firstborn behavioral problems impact sibling relationships

BEER-SHEVA, ISRAEL, September 30, 2025 – A new study from Ben-Gurion University of the Negev (BGU) sheds light on how a firstborn child's behavior after the arrival of a sibling can predict the quality of their sibling relationship over time. The research, published in Social Development (https://doi.org/10.1111/sode.70008), highlights the crucial role of maternal reflective functioning in mitigating negative outcomes, particularly for children exhibiting internalizing behavioral problems.

The study, co-authored by Prof. Naama Atzaba-Poria and Dr. Porat Yakov from BGU's Department of Psychology, followed 117 Israeli families expecting a second child. Data was collected at three points: during pregnancy, 4-6 months after the birth of the second child, and 18 months after the second child's birth.

Key findings from the study include:

Firstborn Behavioral Problems Predict Poorer Sibling Relationships: Firstborn children who exhibited higher levels of internalizing (e.g., anxiety, withdrawal) and externalizing (e.g., aggression, tantrums) problem behaviors 4-6 months after the birth of their sibling had a more negative sibling relationship a year later. This expands on previous research by demonstrating this longitudinal link early in the sibling relationship. Maternal Reflective Functioning as a Protective Buffer: The study found that maternal reflective functioning—a mother's ability to perceive and interpret her child's internal mental states—moderated the relationship between firstborn internalizing behavioral problems and the quality of the sibling relationship. Mothers who were more reflective before the second child's birth were able to mitigate the risk of a negative association between internalizing problems and the sibling relationship. Distinct Roles of Maternal Characteristics: Interestingly, maternal sensitivity (the ability to appropriately respond to a child's needs) did not show the same moderating effect. This suggests that maternal reflective functioning with its focus on understanding and articulating a child's complex emotional experiences, offers a unique form of support during this challenging family transition. Externalizing Problems Less Affected: Maternal reflective functioning did not significantly moderate the link between externalizing problems and sibling relationship quality, suggesting that these behaviors may be more resistant to this particular maternal influence. There may be other maternal behaviors that may buffer child’s externalizing problems.

"The arrival of a new sibling is a significant developmental challenge for firstborn children, often requiring major adjustments," says Prof. Naama Atzaba-Poria, corresponding author of the study and director of The Duet Center at BGU. "Our research underscores the profound impact of a mother's capacity to understand and reflect on her child's inner world, especially when the firstborn is struggling with internalizing behaviors."

The researchers suggest that interventions focusing on enhancing maternal reflective functioning could be beneficial for families preparing for a new baby, potentially facilitating a smoother transition for the firstborn, and fostering more positive sibling relationships.

Additional researchers from BGU included Prof. Florina Uzefovsky, and Dr. Kinneret Levavi. Researchers from the University of Massachusetts and Clalit Health Fund also contributed.

The study was supported by a United States-Israel Binational Science Foundation (BSF) Grant (No. 2016023).

Link to a photo of Prof. Naama Atzaba-Poria (Photo Credit: Dani Machlis/BGU): https://mediagraph.io/shares/306d5952cabac706-prof-naama-atzaba-poria

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