I am the oldest of 5 children, and feel that this quality is important and should be a part of my application. Reasons include my house often being chaotic making it hard to concentrate, learning how to balance school and taking care of younger siblings, managing temper tantrums, etc. I’m having trouble thinking of an organic way to insert this into my application.
Your essay could be a place to mention this, but many applicants are older siblings.
It’ll appear in two places on common app: first, when you list your family, second, when you list extracurriculars (taking care of siblings/family duties is listed and you can elaborate in a few words).
If you feel it is a defining characteristic then you can start off from there for your essay. The topic doesn’t matter, it’s just a starting point. What matters is how well you handle it. Read a lot of long form essays (Wired, Harper’s, The Economist, Washington Monthly, National Geographic, for instance) to see what colleges expect in terms of style. (Hint: evocative, straightforward, mixing action and reflexion.)
Bear in mind that college (both the new independence and the number of others around you) can be chaotic, too. Considering your whole application, do you think having 4 sibs is a selling point? Adcoms can be less interested in this than in the ways you overcame and triumphed.
Remember the essay is for an admit, not an ordinary writing assignment.
As a mother of multiple children, I must say I do think the oldest often takes on so much responsibility -often without being asked. I absolutely think it is worth mentioning if you feel it has shaped you and your upbringing. My oldest is a mediator, caretaker, counselor, even though I am usually present. Does your major match up at all to reflect that? That might be an essay topic?