<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
=== If you do not have JQueryUI ===
The widget will attempt to self load jqueryUI, if this is causing problems you can add it to your page after the jquery script.
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/themes/smoothness/jquery-ui.css">
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>
If you want to optimize, it should be enough just to load the JQueryUI datepicker modules.
The widget can be forced to not attempt to load it's own JQueryUI by setting the following parameter.
loadJQueryUI: false
== Wordpress ==