try this
$children = wp_list_pages('title_li=&child_of=".$post->ID."&echo=0&link_before=<i class="icon-something"></i>');
define link_before property in wp_list_pages
try this
$children = wp_list_pages('title_li=&child_of=".$post->ID."&echo=0&link_before=<i class="icon-something"></i>');
define link_before property in wp_list_pages