The Flight Of the Fluttering Swallows

"Michael Paterniti profiles North Korean teenagers, who have joined swelling ranks of young people embarking on perilous journey to China, where they make their way to South Korean consulate to defect; those who make trip do so knowing they can be sent to prison camp or killed if they are caught; it is estimated that there are nearly 10,000 North Korean child refugees in China, but only about 100 of them have completed journey to South Korea in last five years; many who have arrived in South Korea live in terror of being found, and human rights groups say families of defectors are often severly punished; integration of refugees into South Korean society discussed; drawings (L)"