Why? So that girls who wear that size can't find clothes?

It is possible to wear a size 0 and still be healthy.

In pants I wear a 0 or a 1, depending, and I'm not unhealthy. I also don't starve myself to be that size, I just don't have hips or a butt really. I probably eat more than the majority of girls who weigh more than me, I'm eating right now actually, but I have a very fast metabolism and I'm quite active.

Most younger teenagers will probably be around that size as well because typically you gain weight as you get older and your body begins to develop more. I'm not a younger teenager, I'm on the older spectrum of teenagers, and my body has developed, but as stated before I have small hips and a fast metabolism.

I'm not unhealthy just because I can fit into pants of a size 0 or 1, anyone who would look at me would most likely think that I am healthy and probably think that I weigh more than I do, because well, I am healthy.

Obviously not every girl who wears a size 0 is naturally that skin, but that's usually more likely in taller and older females, such as some fashion models. However, not all models are a size 0(typically a 2 or a 4), and a lot actually are at healthy weights for the their heights. A lot of models are under 18 as well and still developing so for them being at a small size would be naturally.

However, the ones that do starve themselves or do other things to stay skinny do not send a positive message.

Edit- oh and a size 0 probably isn't as small as you may think it is, because of vanity sizing what's now known as a 0 is actually bigger than it is. Vanity sizing has clothes marked down a few sizes smaller than what they really are.

Edit 2- As for the comment about a 0 being child size, I really do take offense to that in a way. As stated earlier pants wise I wear a 0 or 1, but I still have curves. I actually probably have a more womanly shape and curvier body than most females my age, even the ones who are larger than me.