My wife and I used to do some seminars for couples getting married. One of the exercises we ran them through was a demo on how birth order affects your outlook. We divided them into groups - oldest/only, middle, and youngest children and had them put together a list of what being an oldest/middle/youngest meant to them.
We'd then meet and go over the lists and give our observations on how the groups interacted.
Oldest children (I am one), tend to be very anal. They'd stand around eqidistant from each other in a perfect circle. Everyone would get to provide input, and they'd make the longest lists - often 30/40 items. They never had enough time to finish their list. They kept frowning at the group of youngest children. And kept one eye on the clock.
If you ever want to screw with an oldest child, do something different that they're not used to - e.g. drive them on a different route to school - put a forum topic where it didn't used to be. Almost immediaely they ask " What are we doing? Why?"
Youngest children would lay around all over the place and talk about everything but the list. At the last minute, they'd toss something together. They didn't look at the clock or any other group.
The group of middle children would spend most of their time watching the other two groups. They were pretty silent.
The moral was to use each others personal outlooks to enhance the relationship like when grocery shopping. An oldest child will have a grocery list and run through the aisles the same way everytime. A youngest will not have a list, will wander the store, and will probably forget some "essential" items, but will pick up something they haven't tried before from the shelves. Two middle children are often going to have a tough time making a decision if neither has been on their own (pseudo-oldest) for a while.