The "parent category" is called "Veiligheid" and has ID 992504. That category is empty, because the products are in the subcategories: 994433, 994434, 994435 and 994436. I want to show the products from the subcategories on the page Veiligheid (in the dropdown filter).
So I started with the following code, which shows the products from 994433 on the page Veiligheid. However, I want to show 34, 35 and 36 as well. I've added the line you've suggested and placed it on several ways, but that didn't work. I'm sure I'm doing something wrong, so I was hoping you could tell me how to change the code below.
<p style="font-family: Play; font-size: 18px; margin-bottom: 10px;">Selecteer merk</p><select name="brand">
<?php echo dfr_get_brands($cat_id='994433'); ?>
<p style="font-family: Play; font-size: 18px; margin-bottom: 10px; margin-top: 10px;">Selecteer webshop</p><select name="merchant_id">
<?php echo dfr_get_merchants($cat_id='994433'); ?>
<p style="margin-bottom: 20px;"></p>
<input type="submit" value="Zoeken" />