JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="mainMenu">
    <li>Main
        <ul class="subMenu" id="m1">
            <li>Sub</li>
            <li>Sub</li>
            <li>Sub</li>
            <li>Sub</li>
        </ul>
    </li>
    <li>Main 2
        <ul class="subMenu" id="m2">
            <li>Sub</li>
            <li>Sub</li>
            <li>Sub</li>
            <li>Sub</li>
        </ul>
    </li>
</ul>

CSS

.subMenu {
    display: none;
}

JavaScript

$('.mainMenu').children('li').on('click', function() {
  
  /* $(this).children('ul').slideToggle('slow') */; 
});