I read ChinaSmack, a blog about various scandals of corruption and violence in China (of which there are a huge number). Today there was a post about the kidnapping of children: every year, tens of thousands of children are stolen from their families and sold on the black market, for use as child beggars, for prostitution, for forced marriage, and perhaps most relevantly for Westerners, for adoption. This website gives a brief overview of the problem, including snippets of heartbreaking interviews with parents (very few children are ever found).
The sale of stolen children to new adoptive parents has a long history in China; it's an important plot point in Cao Xueqin's Story of the Stone, which dates from the 18th century. And it continues unabated today; although the scale of the problem is not clear (as the Chinese government does its best to hide it), it could be as many as 70,000 each year.
In the West there have been occasional stories about these problems, but for the most part people are unaware. Thousands of Chinese children are adopted by Americans every year, and it is likely that at least some were kidnapped, or at best removed by coercion from loving parents.
China is not exceptional in this regard. Most other developing countries have similar problems, including India, Guatamala, Ethiopia, and most other popular sources of children for international adoption. If you are adopting a young child or infant internationally from a poor, corrupt country, there is simply no way to know if they were stolen.
As a result, I believe that international adoption is a terrible idea. While most people adopting think they are benefiting the children involved, the truth is much murkier. They may simply be enriching child thieves and destroying loving families while in pursuit of their own. By adopting, they are participating in an unjust and criminal system.