$children_category = array(
    'child_of'           => $category_id,
    'style'              => 'none',
    'orderby'            => 'slug',
    'hide_empty'         => 0,
    'exclude'            => '1',
    'use_desc_for_title' => 1,
    'hierarchical'       => 1,
    'title_li'           => '',
    'echo'               => 1,
    'depth'              => 0
   );
$fncat = wp_list_categories($children_category);