Weir (2022) wrote an article in the Monitor on Psychology attesting to the importance of sibling relationships for personal development. More children in the United States live with siblings than with their fathers. Children spend more of their time out- of- school with siblings than with any others, including parents and friends. Over the course of their lives, siblings are those family members with whom a person will share the most years. Therefore, siblings can understand one another in ways others cannot. No one knows better what it was like to grow up within one's family of origin.
When young, siblings can be positive influences by supporting and learning from one another. Warm relationships can help buffer against bullying from peers and from parental anger. Negative impacts come when children compete for the attention of their parents and if they model risky behaviors, like substance use and sexual acting out. There can be many combinations of the positive and negative.
In young adulthood, siblings often get along better with one another. Their support at this stage matters as much as peer and parental support. As full adults, they maintain their mutual influence. Good relationships provide needed benefits. Conflicts among siblings can contribute to depression and substance abuse. As they age, the influence remains. There are often high levels of warmth and low levels of conflict, especially in sister-sister pairs.
Parents would benefit their families by fostering positive sibling relationships. Weir's article made several suggestions. Being careful not to favor one child over another and not to compare siblings are best. It is helpful not to take sides in sibling arguments, but instead it is helpful to coach children on how to resolve conflicts. Also, it is recommended that positive feedback be given when siblings are doing well together.
Reference
Weir, K. (2022). Improving sibling relationships. Monitor on Psychology, 53(2), pp. 60-67.