JSFiddle - React, Tailwind, and code Playground

HTML

<ul>  
         <li><input type="checkbox" level="child"  name="somename3" value="1" /> Child 1</li>
         <li><input type="checkbox" level="child"  name="somename4" value="2" /> Child 2 <br />
				<ul>
                    <li><input type="checkbox" level="subchild" name="somename1" value="3" />Sub Child 1</li>
                    <li><input type="checkbox" level="subchild" name="somename2" value="3" />Sub Child 2</li>
				</ul>
		 </li>
         <li ><input type="checkbox" level="child"  name="somename3" value="3" /> Child 3</li>
     </ul>

JavaScript

$('input[type=checkbox][level="child"]').on('click', function () {
        var checked = $(this).is(':checked');
        
        // go up the dom to the parent of checkbox (li)
        $(this).closest('li')
        
        // find all subchild checkboxes
        .find('input[type=checkbox][level="subchild"]')
        
        // make them as the parent checkbox (checked or not)
        .prop('checked', checked);
    });