$("#birthdate").datepicker({
            changeMonth: true,
            changeYear: true,
            altFormat: 'dd-mm-yy',
            altField: '#birthdate',

             });

$("#birthdate #alternateDate").datepicker({

$.datepicker.formatDate('dd-mm-yy');
            $(".datepicker").datepicker({
                changeMonth: true,
                changeYear: true,
             });

<label for="geboortedatum">Geboortedatum <em>*</em></label><br/><input type="text" class="datepicker" id="birthdate" name="birthdate" value="{$birthdate}"><br/>

<input type="text" id="birthDate" class="MyDatePickers">
<input type="text" id="alternateDate" class="MyDatePickers">

$(".MyDatePickers").datepicker({
                    changeMonth: true,
                    changeYear: true,
                    dateFormat: 'dd-mm-yy'
                     });