Firstborn Behavioral Problems Predict Later Sibling Relationship Quality: The Moderating Role of Maternal Sensitivity and Mind‐Mindedness

Our study investigated the link between a firstborn child's behavior after the birth of a sibling and the quality of their sibling relationship over time, while considering the moderating role of maternal sensitivity and mind‐mindedness. This study included 117 Israeli families expecting a second child. Data were collected at three time points: during pregnancy, 4–6 months after the birth of the second child, and 18 months after the birth of the second child. Results indicated that firstborn children ( M age = 24.6 months, SD = 7.42; 59 girls) who exhibited higher levels of internalizing and externalizing problem behaviors at 4–6 months after the birth of their sibling also had a more negative sibling relationship a year later. Maternal mind‐mindedness, but not maternal sensitivity, moderated the relationship between firstborn behavioral problems and the quality of the sibling relationship. However, this protective effect was limited to internalizing, but not externalizing, behavioral problems.