[Plugin: Events Calendar] Filtering by Parent Categories

I have a some categories set up like so:

Age
Child
Teen
Adult
Language
English
Spanish
French
Where Age and Language are parent categories, and those following are child categories.

Relevant code below:

$cat = (isset($_GET['cat'])) ? $_GET['cat'] : 0;
$args = array(
            'tax_query' => array(
                array(
                    'taxonomy' => 'tribe_events_cat',
                    'field' => 'id',
                    'terms' => $cat,
                ),

            )
    );
    $my_query = new WP_Query($args);

Right if I choose Child and Teen it will display all posts tagged with Child OR Teen, which is desired. But if I also choose Spanish, it will display events tagged with Child OR Teen OR Spanish.

How can I fix my query so that if I choose Child and Spanish, it will pull posts tagged with Child AND Spanish instead of posts tagged with Child OR Spanish?