How Birth Order Affects and Sibling and Family Dynamics
No matter when you were born, or who you've become, it is important to accept each person for who they are as an individual. It is important that we not assume we know someone because they fit into certain categories such as "first-born" or "only-child." That being said, there are some common threads that often appear in an individual's personality or propensities or sibling relationships, relating to their birth order.
The eldest child usually has received the most focused attention from her (or his) parents during those vital formative years. If the family is healthy and loving, this often means that child is the most advanced and the most capable of taking on additional responsibilities or expectations. The eldest often feels responsible. The eldest is often driven to succeed.
The eldest also often has the highest expectations and the toughest rules placed on him or her. They are the ground-breakers. The one the parents are learning on. Parents usually relax a bit on the later children because they have a better understanding of what's important to them as a parent, because there are more places for their limited attention to go, and because they have (and expect) the eldest child to help out.
As adults, we see these characteristics retained, and the oldest child may continue to have rigid expectations of themselves and of what "right-behavior" looks like. Eldest children are often care-takers, especially in healthy loving households. I'll get to common realities for children and grown-up children of unhealthy homes in a minute.
The next-oldest child often shares many of the responsibilities, without the benefit of any special privileges that the oldest sibling receives. The second child is not seen as the oldest, the smartest, the... They often feel left out or over-burdened. The "ugly step-child" who never quite has enough, and doesn't know how to ask for more. This child is often driven to prove him or herself, usually against the accomplishments of the eldest, or the perceived expectations (not the same as the actual expectations!) of the parents.
The second-oldest may go out of his/her way to be different from the eldest, or may give up on meeting any expectations, and act laid-back and fun-seeking (while somehow remaining disengaged from life and goals). Sibling children who are close together in age often take one of two routes-- either they are best friends and share everything, or they don't get along at all and want to emphasize their differences.
This relationship between first and second-born primarily depends on the eldest child. Is he/she able to enjoy having a live-in best friend without expressing superiority or a need for special recognition as the oldest? Or has she/he embraced the role of "third-parent" to the point that she/he resents the efforts of the second oldest to copy or equal him/her? The oldest may even feel that his/her role in the family is threatened by the second-oldest child's efforts to take on some of the "older child" responsibilities and power in relation to the younger children.
At the same time, that second-oldest may feel that they are never good enough, or that they must take on the same role with the family that the eldest had, when he/she finally leaves home and the second gets to be the "oldest." They can be very disappointed when the skills and responsibilities and special rights they have so carefully practiced are no longer needed or appreciated now that everyone is older, and the eldest has moved out.
In a three-child family, the youngest is the peace-keeper and the comedian. It's his/her role to act the clown, to get attention by being funny or acting out, and to smooth over rifts among other family members either by pulling attention to herself or acting as a peace-maker directly. The youngest child in a family often gets more attention during the critical formative years because there is no new baby to "replace" him or her. Also, for each additional child, the parents' attitude and rules usually relax even further.