i am serching a WP function that controls is there any child category/ies of current category (in category.php outside of the loop) and if there is, just add link list for that category/ies to page, otherwise (there is no child category for current) list all post(s) in this category. Thanks in advance...
You can get the current posts category outside the loop by using the get_the_category function. http://codex.wordpress.org/Function_Reference/get_the_category
When you have the actual category ( however you got it) you can use get_categories, specifically the 'child_of' parameter and pass it the parent cat ID. http://codex.wordpress.org/Function_Reference/get_categories
Also have a look at wp_list_catagories, http://codex.wordpress.org/Template_Tags/wp_list_categories#Display_or_Hide_the_List_Heading where you can do something simple like the following to grab the children.
<?php wp_list_categories('orderby=id&show_count=1&use_desc_for_title=0&child_of=8'); ?>
You would probably do an "if" statement to get the children if they exist and if not just show the category.