Am gasit ceva apropiat pentru ce am cautat, insa se pare ca "wp_dropdown_categories" nu functioneaza cum trebuie.
Codul folosit este urmatorul:

<form role="search" method="get" id="searchform" action="<?php bloginfo('home'); ?>">
<fieldset class="searchdropdown">

Age:
<?php wp_dropdown_categories('child_of=19&orderby=name&h ide_empty=0&show_option_all=All&selected=true&hier archical=1&taxonometry=category'); ?>

Country:
<?php wp_dropdown_categories('child_of=16&orderby=name&h ide_empty=0&show_option_all=All&selected=true&hier archical=1&taxonometry=category'); ?>


Project type:
<?php wp_dropdown_categories('child_of=25&orderby=name&h ide_empty=0&show_option_all=All&selected=true&hier archical=1&taxonometry=category'); ?>


<input type="text" value="<?php echo wp_specialchars($s, 1); ?>" placeholder="Enter term or leave blank" name="s" id="s" />
<input type="submit" id="searchsubmit" value="Search" />

Exemplul facut de mine este aici

Are cineva idee daca gresesc undeva sau daca trebuie adaugat ceva in functions ?
Merci