--- a/term_reference_tree.module
+++ b/term_reference_tree.module
@@ -139,7 +139,7 @@ function _term_reference_tree_get_children($tid, $vid) {
   $query = db_select('taxonomy_term_data', 't');
   $query->join('taxonomy_term_hierarchy', 'h', 't.tid = h.tid');
   $query->join('taxonomy_vocabulary', 'v', 'v.vid = t.vid');
-  $query->fields('t', array('tid', 'name'));
+  $query->fields('t', array('tid', 'vid', 'name'));
   $query->addField('v', 'machine_name', 'vocabulary_machine_name');
   $query->condition('t.vid', $vid);
   $query->condition('h.parent', $tid);