<script type="text/javascript">

    $(document).ready(function(){

        $('select.ParentCategoryID').change(function(){

            var val = null;

            if($(this).val()){
                val = $(this).val();
            } else {
                val = $(this).prev('select.ParentCategoryID').val();
            }

            $('div#ProductFamilyCategoryContainer').load('<?php echo Router::url(array('controller' => 'productCategories','action' => 'selects')); ?>/' + val);

        });

    });

</script>