Which online shopping website for example, Hot Topic. But I want
a website that has metal/rock band t-shirts for kids around 10~12.
And the site needs to include international shipping.

Here is a reputable site with rock/punk clothing for Kids available:
http://www.punkbabyclothes.net

You can view the international shipping options on their site by going here:
http://www.punkbabyclothes.net/shipping.html
If you don’t see the country that you need on their shipping list, you can forward your items through a forwarding service that has shipping to over 223 countries worldwide.

Here are a couple of forwarders to check out if need be:
http://www.bongous.com
http://www.usa2me.com