One of the strongest influences I see in real life are siblings, yet I almost never see convincing siblings in fiction any more. Meg without Charles Wallace would be neurotic instead of a caring big sister.
I'm number two in a family of five. My older brother beat up boys who thought I was cute. My sister and I shared a room. The two youngest were born when I was a teenager and were very effective birth control. When I sit down to write, I ought to draw on those experiences, on chaos of a large family. Instead, I do everything I can to keep my MC alone. I send older siblings away to college, wrap up younger siblings in activities, write characters who are only children, all to avoid one of the richest sources of character development.
Birth order theories can be a great way to add some depth to your characters - and flesh out their families. We all know "lonely-onlys" and melancholy middle children (hem, me), but there's a lot of research into birth order - why not use it? Here's a quick run down of some stereotypical birth order characteristics:
The oldest sibling is an only child first and knows what it's like to be the center of attention in ways subsequent children don't. They want to be right and in control. They're leaders and often protective. They are often more conformist, striving to please. First borns are reliable, conscientious, structured, cautious, controlling high achievers.
The second child seldom has his or her parents' undivided attention and is always behind a more advanced older sibling. In a sense, they are born playing catch up. Often, if the first child is a high achiever, the second will act out to gain attention and almost always develops skill, interests and abilities their older sibling does not exhibit. In other words, they aim for the opposite of their older sibling, especially if they're the same gender.
Particularly in a family of three, the middle child gets squeezed. Neither the first nor the baby, middle children often feel left out and like they lack a place within the family. However, middle children are also adaptable. They are skilled negotiators, dealing with older and younger children. Middle children are people-pleasers, yet rebelious. They thrive on friendship and have large social circles. They're peacemakers.
The baby of the family often acts like an only child with extra parents. Everyone is bigger and more capable, so they abdicate responsibility, letting others make decisions on their behalf. Parents are often more relaxed, so the youngest will get away with more than older siblings did at the same age. Youngest children are fun-loving, uncomplicated, manipulative, outgoing, self-centered attention seekers - and everyone loves them for it.
Only children grow up surrounded by adults. They may be pampered, or at least are the center of their parents' attention, but also must learn to entertain themselves. Only children are mature for their age. They are conscientious, diligent perfectionists. They make great leaders.
There are a lot of exceptions to these rules and they go much deeper than this post will allow, but it's a quick start into a fascinating area of study. If you want more characteristics, exceptions and info on how gender and spacing effect birth order, look here and here for some fun charts.
Siblings are a lot of fun in real life and should be fun to write! Go explore ways to bring those relationships into your writing.
Also, because I'm nosy like this, how do you compare to your birth order traits? Anyone care to argue for why their stereotypes are wrong?