JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.13.1/jquery.validate.js"></script>
<form id="myform">
    <select name="child_class" class="drop-select-2">
        <option value="">Choose...</option>
        <option value="1">1</option>
        <option value="2">2</option>
    </select>
    <input type="submit" />
</form>

JavaScript

$(document).ready(function () {

    $("#myform").validate({
        rules: {
            child_class: 'required'
        }
    });

});