Impact of Firstborn Behavioral Issues on Sibling Relationships and the Role of Maternal Reflection

A recent study conducted by researchers at Ben-Gurion University of the Negev (BGU) has provided valuable insights into how a first child's behavior after a new sibling arrives can influence the developing sibling bond over time. The research emphasizes the significance of maternal reflective functioning—the mother's capacity to understand and interpret her child's internal mental states—in mitigating potential negative effects, especially for children displaying internalizing behavioral problems such as anxiety or withdrawal.

This longitudinal study, published in Social Development, tracked 117 Israeli families expecting their second child, collecting data during pregnancy, 4-6 months after birth, and 18 months post-bregnancy. The findings revealed that firstborn children exhibiting higher levels of internalizing behaviors (e.g., withdrawal, anxiety) and externalizing behaviors (e.g., aggression, tantrums) shortly after the sibling's arrival tended to have poorer sibling relationships a year later. Interestingly, maternal reflective functioning played a moderating role; mothers with higher reflective capacities before the second child's birth were better able to buffer their children from developing strained sibling interactions. In contrast, maternal sensitivity—the ability to appropriately respond to a child's needs—did not show the same moderating effect, highlighting that understanding and articulating a child's emotional inner life is particularly crucial during family transitions.

The study also found that maternal reflective functioning did not significantly impact the relationship between externalizing behaviors and sibling bonds, suggesting different underlying factors. Expert Prof. Naama Atzaba-Poria emphasizes that the arrival of a new sibling presents significant developmental challenges for the firstborn, requiring substantial adjustments. Enhancing maternal capacity to reflect on her child's mental states could be pivotal in promoting healthier sibling relationships.

Researchers propose that interventions aimed at improving maternal reflective functioning may ease this transition, fostering more positive interactions among siblings. Additional experts from various institutions contributed to this comprehensive study, underscoring its importance for family dynamics and child development.

source: https://medicalxpress.com/news/2025-09-firstborn-behavioral-problems-impact-sibling.html