To be honest that even makes sense. Children grow up too fast and have to buy new clothes almost every month or two. In addition to that, they are sloppy, and while playing they tend to rip their shirts or pants, or whatever. With that said, clothing companies make clothes for children more expensive since people have to buy more often for their kids than for themselves.
Its true that kids clothes are costlier than adult clothes. This is due to the fact that smaller items require more skill and precision to construct. This applies to other items too. Many parents in my area opt to solicit used uniforms for their children as they grow older instead of buying new ones as kids rapidly outgrow them due to increase in height and girth. In many cases, parents acquire them for free.
I think that this may be one of the downsides of the online shopping buzz. For whatever reason I have not seen that many of the clothes donations stores any more, and I am not sure if they are related or not but those were huge in getting some cheap kids clothes when they were in need.