If you grew up with siblings or have multiple children, you probably understand the major effect that birth order has on family dynamics. We all know the stereotypes about how oldest, middle, and youngest children likely behave and what their place in the family means about their future achievement and success. Everyone probably has a story about how they were impacted by older or younger siblings and how they were treated differently by their parents. I could probably write a book on my opinion and experiences with birth order and family dynamics (middle child here!), but I really wondered how much birth order impacts a child's development and the way parents interact with their children.
There have been a lot of studies done on how birth order affects personality, intelligence, and achievement. Many researchers have found that the oldest child in a family is likely to have higher intelligence and perform better in school than subsequent siblings, probably because they were the only child for a period of time and received all of their parents' attention during infancy and early childhood. Studies focusing on birth order and personality have found that older siblings tend to be more motivated to live up to their parents' expectations, while younger siblings are less worried about meeting their parents' expectations and tend to be more rebellious. However, these findings are controversial, since some studies have found relationships between birth order and these personality or achievement outcomes, while other studies have found no effect at all.
Research suggests that there may be some benefits to having siblings. Children with older siblings may reach developmental milestones faster, because they are watching their older brothers or sisters and eager to keep up with what they're doing. Children with siblings also may develop better prosocial skills than only children, such as sympathy, taking turns, listening, cooperating, dealing with conflict, and being patient. One study also found that having siblings can be protective against depression and low self-esteem as an adult. Only children, however, may be more creative than children who grow up with siblings.
After reading several articles about birth order, it seems to me like there's no conclusive research about how siblings and birth order affect child development. After all, every family and every child is so different! It may be true that the oldest siblings get a little more one-on-one time with parents in early childhood, but younger siblings get the benefit of a more relaxed, experienced parent. There are pros and cons to being an oldest child, a middle child, a youngest child, and even an only child. I really think that parents do their best to give each child what he or she needs, and it may be helpful to try to limit comparison between siblings, as difficult as that may be.
If there's a lot of rivalry, jealousy, or comparison between your children, it may be helpful to try giving each one individual special time. Special time is one-on-one interaction between a child and parent for as little as 10-15 minutes, where the child gets to choose what they do and the parent gives his or her undivided attention for that period of time. Setting aside just a little bit of special time for each of your children every week can help them feel much more content, loved, and appreciated, and it can be helpful for lots of behavioral issues.
For more information about how birth order impacts children and families, check out these articles:https://www.psychologytoday.com/us/blog/the-baby-scientist/201804/does-birth-order-matterhttps://www.parents.com/baby/development/social/birth-order-and-personality/