$array = array();
get_sons($type, $array);

var_dump($array);

function get_sons($type, &$current_array){
    $result = mysql_query("select id from dede_arctype where reid = {$type}");
    while($row = mysql_fetch_assoc($result)){
        $current_array[] = $row['id'];
        get_sons($row['id'], $current_array);
    }
}