Size what?

I don't understand the sizes anymore. There's a size zero, which I didn't even know that they had. It must stand for: 'Ohhh my God, you're thin.'
- Ellen DeGeneres

I have four children, two are young (5 &8) two are TEENAGERS. Going shopping with the younger ones makes sense...the older two, not so much. Today, after our garage sale we made a trip to the resell shop to see if they would buy any of their name brand items before we donated them to a local charity. The requirement for the shop, as they evaluate your stuff to see if it's worthy of their shop, is that you must remain in their store until they can call you up to tell you how much (or how little) they will pay you for your items. I understand, they have much to do, like go through everything to see if they want it first before putting it out on the sales floor, often for 5x what they paid you for it {side note...we found a skirt that my daughter sold them last week for $2 marked $10 on a rack...the exact skirt that still had her intitials on the tag}.
But I digress...(and I obviously have decided to use way too many ...'s) As we wandered the store while they picked through our baskets of clothing I had a chance again to ponder the sizing of teens clothing, and I'm not referring to midriff baring tops nor butt revealing mini-skirts. I am talking about clothes that are sized "0" or even "00" and "xs, xxs, and even one xxxs" not to even mention all the size "1, 2, and 3's" that look like my five year old should be wearing them. I know I'm a bit on the mature side of age, but when I was a teenager I do not remember there being clothes that were smaller than 5's when it came to girls in school...and its not like there weren't thin girls, I was a seven and I know I was normal sized. It seems like maybe we are just steps away from sizing clothes into oblivion.