How to link Children categories?

Hi there,

I want the Post thumbnails to link to the a specific Children category. For example I have:

Rock
–Blues
–LiteRock
–HeavyRock

And the post have been assigned to both Rock and ONE of the three children category (for example LiteRock).

I’m currently using this:

<?php foreach( ( get_the_category() ) as $categoryz) { $categoryz->cat_name . ' '; } ?>

<a href="<?php echo get_category_link(get_cat_id($categoryz->cat_name)); ?>">
<img ... />
</a>

And it works, but I actually find that WordPress choose alphabetically the one that comes later, and so Rock comes after LiteRock.

So I have the link for the Rock parent category. Any ideas?