Parents marched on Sunday, holding pictures of their lost children, often their only one because of China's population-control policy. The protests threaten to undermine the government's attempt to promote its response to the quake as effective. But authorities in Beijing appear to have recognized the delicacy of the issue, and officials have expressed strong- worded statements vowing to find those guilty of cutting corners on school constructionParents marched on Sunday, holding pictures of their lost children, often their only one because of China's population-control policy. The protests threaten to undermine the government's attempt to promote its response to the quake as effective. But authorities in Beijing appear to have recognized the delicacy of the issue, and officials have expressed strong-worded statements vowing to find those guilty of cutting corners on school construction