#I'm getting: Use of uninitialized value in string comparison (cmp) at /usr/local/perl/lib/site_perl/5.12.2/XML/Twig.pm line 9313.
my $t = XML::Twig::Elt->new();
->parse( \*DATA);
$t->sort_children(); #Child
$t->print;

__DATA__
<?xml version="1.0" encoding="utf-8"?>
<root>
        <parent attribute="info1">
                <Child4>
                        <childinfo Number="1" attrib2="info3"/>
                </Child4>
        </parent>
        <parent attribute="info1">
                <Child5>
                        <childinfo Number="1" attrib2="info3"/>
                </Child5>
        </parent>
        <parent attribute="info3">
                <Child1>
                        <childinfo Number="3" attrib2="info3"/>
                </Child1>
        </parent>
        <parent attribute="info1">
                <Child9>
                        <childinfo Number="1" attrib2="info3"/>
                </Child9>
        </parent>
        <parent attribute="info5">
                <Child7>
                        <childinfo Number="5" attrib2="info3"/>
                </Child7>
        </parent>
        <parent attribute="info4">
                <Child1>
                        <childinfo Number="4" attrib2="info3"/>
                </Child1>
        </parent>
        <parent attribute="info1">
                <Child12>
                        <childinfo Number="1" attrib2="info3"/>
                </Child12>
        </parent>
        <parent attribute="info1">
                <Child10>
                        <childinfo Number="1" attrib2="info3"/>
                </Child10>
        </parent>
        <parent attribute="info2">
                <Child8>
                        <childinfo Number="2" attrib2="info3"/>
                </Child8>
        </parent>
        <parent attribute="info1">
                <Child6>
                        <childinfo Number="1" attrib2="info3"/>
                </Child6>
        </parent>
        <parent attribute="info1">
                <Child3>
                        <childinfo Number="1" attrib2="info3"/>
                </Child3>
        </parent>
        <parent attribute="info1">
                <Child2>
                        <childinfo Number="1" attrib2="info3"/>
                </Child2>
        </parent>
</root>