WASHINGTON -- Hours after President Obama signed historic health care legislation, a potential problem emerged. Administration officials are now scrambling to fix a gap in highly touted benefits for children. Obama made better coverage for children a centerpiece of his health care remake, but it turns out the letter of the law provided a less-than-complete guarantee that kids with health problems would not be shut out of coverage. Under the new law, insurance companies still would be able to refuse new coverage to children because of a pre-existing medical problem, said Karen Lightfoot, spokeswoman for the House Energy and Commerce...