Include child categories in event category queries

// Let's inspect the parameters of any event queries
add_action( 'tribe_events_pre_get_posts', 'tribe_query_include_child_cats' );

/**
 * Modifies the taxonomy part of an event query and ensures child categories are included.
 *
 * @param $query
 * @return mixed
 */
function tribe_query_include_child_cats( $query ) {
    // If the tax_query is not specified do not interfere
    $tax_query = $query->get( 'tax_query' );
    if ( ! is_array( $tax_query ) ) return $query;

    // Look for include_children flags and set to true
    foreach ( $tax_query as &$component ) {
        if ( is_array( $component ) && isset( $component['include_children'] ) )
            $component['include_children'] = true;
    }

    // Update the query
    $query->set( 'tax_query', $tax_query );
}