As a younger sib, you really get the shaft. My disorganized sister regularly rifled my school supplies. OK, you could say they weren't mine, but it was a notebook I took to school everyday that I could find it! Over and over, I'd go to bed (little kids have early bedtimes), only to find my homework/schoolbooks/ school projects rifled for older sibs needs.
I probably was too vague in my response. My kids would be in HUGE trouble if they took their siblings school supplies, or borrowed a bike that was needed to get to work! And if one of my dds (22 and 19) bought a car, I'd definitely expect that the other one would not borrow it without some express permission. I tried to differentiate between toys (the legos, or train set, or basketballs) which are pretty much shared, and clothes, for example, or make-up. Part of it also is that I set the rules for ds12 and ds10, but I don't set the rules for the older kids (beyond basic household/roommate expectations when they're here). Absolutely!!! - if a teen buys clothes or a bike or whatever (or gets them as a gift)- a sibling shouldn't be allowed to just take them. What I'm saying is when we have a playroom full of toys, most of which neither boy can remember who "owns," (again, they share a bedroom, a playroom, a desk and a Wii :)), it's silly to be arguing about a ball that one kid wasn't using but thinks is his.
Our oldest dd is very disorganized and I've made it 100% clear in the past that she can't "borrow" someone's keys because she's lost hers, or grab someone's graphing calculator because hers in in her messy room somewhere, or take her sister's curling iron to a sleepover because she didn't replace her broken one.
To me, the original post wasn't about sharing actually, it was about just being a nice person. Letting your sibling take your favorite sweater, that you planned to wear, because she didn't do any laundry- that's letting yourself get walked over (and parents should help the kid learn to stand up for herself). Not letting your sibling use a ball that won't in any way be "lessened" or used up when you're not doing anything with it is just being a little jerk (maybe not if you're five, but that's why parents step in and teach them that this is not nice behavior).
Anyway, everyone has different lines, and I'm sure we're all influenced by how we grew up, but I want my kids to learn to be kind and generous without being taken advantage of. There is a middle ground I think....
