Something else I don't think people quite get is the level of secrecy, trust, and all-around reliance I have with my siblings. See, if you leave out the two youngest kids, nobody's ratted anyone out to my parents in at least 5 years. You have to leave out the two youngest because they're 11 and 14 and still into tattling on each other, but for the purposes of this discussion, they're not important.
So, 5 years (at least). We do not tell our parents each other's secrets. Period.
From my dealings with those who have fewer than 4 siblings, I've noticed that, occasionally, you might tell your sister something in confidence and she ends up telling your mom -- to get back at you for something, I guess.
We do not do that. The 5 oldest children in my family make up a tight circle of undying trust and secrets and dark shadowy pasts -- and none of these ever leave the circle. We do not tell our parents, we do not tell our two youngest siblings (because we don't trust them to enter the circle yet), we do not tell our friends, we do not tell our significant others [I think; this has yet to be tested in my case.].
This circle is so tight that, recently, I was told something by One, sworn to secrecy, and did not even bring it up with Three through Five* until checking with One to see who she'd told. S-One** does not believe in this circle of trust, and thinks that if One tells somebody something, soon everyone in the entire family, parents included, will know about it, but the previous example should demonstrate the folly of this viewpoint. If I'm not talking about One's secret with Four until I'm damn sure she's already heard about it from One, there's no way our parents are getting involved, even accidentally.
*We have an odd way of looking at ourselves in that we sometimes refer to each other as our sibling order in numerical form. Ex: I am the second child, hence I am Two. Sex has no bearing on this order, so Jim, the fifth child but first son, is still Five. This system is related to the Baby System (more on that later) and also spawned Odds and Evens [if you can't figure it out, I'm not bothering to explain it to you]. This was also very handy for clandestinely referring to Six and Seven in their hearing -- until they were old enough to figure it out, unfortunately.
**S-One is, not in any way intuitively [which is why I'm explaining it], the spouse of One. He is older than One, and so could bump One out of the one spot, but it was decided by a 5-1-1 vote that this method of adjustment would get inanely complicated with the addition of each new spouse; additionally, it is silly to refer to people as one thing for their entire lives up to the point of marriage then abruptly change that label [this portion of the resolution was approved unanimously]. We went with spouse instead of husband/wife for simplicity; we wanted S1 to be obviously One's husband as S5 is obviously Five's wife and not muddle things up with H1/W5 -- also the original system ignored sex, so, parity. We also had to deal with the arrival of One's children, which resulted in 1.1, 1.2, and 1.3 [my children will be 2.1, 2.2 etc.]. Depending on how ridiculous our kids turn out to be, this could get really complicated, really fast [i.e. my great-grandkid could end up being 188.8.131.52].***
***When I refer to votes, agreements, and decisions, I am not speaking metaphorically or of tacit general agreement. We actually sat down and worked this shit out.