get category name and children category name on different page

Hi Guys !

i have a menu with catgory and (multiple) children category.

they are identic as my menu.

i want to have on ma category page :

the title of the parent category (ex : apple)
the title of the children category (like the menu) (ex : iphone)

i use this code :
<p>Category: <?php single_cat_title(); ?></p>

but i always have only the catgory title where i am, not the parent and/or the children.

with this code i don’t have the good result two.

<?php //echo(get_category_parents($cat, false, '<br />, ')); ?>

on the iphone page for exemple i want to have :

category : apple
sub category : iphone

is someon as an idea i don’t have find the answer since few days on the wordpress codex,

thanks !