JSFiddle - React, Tailwind, and code Playground

HTML

<a title="Filter Category" id="general" class=""><i>Count the checkboxes <small class="counter"></small></i></a>
<div id="video-filter-container">
    <div id="general-content" class="video-filter-content">
        <ul id="general-ul" class="wpuf-category-checklist">
            <li id="category">
                <label class="selec"><input type="checkbox" class="select_all"  /> .Select_all Foo</label>
                <ul class="children">
                    <li id="category-4"><label class="selectit"><input value="4" type="checkbox" name="wpmm[]" id="in-category-4"  /> Foo1</label></li>
                    <li id="category-112"><label class="selectit"><input value="112" type="checkbox" name="wpmm[]" id="in-category-112"  /> Foo2</label></li>
                </ul>
            </li>
            <li id="category">
                <label class="selec"><input type="checkbox" class="select_all"  /> .Select_all Bar</label>
                    <ul class="children">
                        <li id="category-3">
                            <label class="selectit"><input value="3" type="checkbox" name="wpmm[]" id="in-category-3"  /> Bar1</label></li>
                        <li id="category-115"><label class="selectit"><input value="115" type="checkbox" name="wpmm[]" id="in-category-115"  /> Bar2</label></li>
                        <li id="category-114"><label class="selectit"><input value="114" type="checkbox" name="wpmm[]" id="in-category-114"  /> Bar3</label></li>
                </ul>
            </li>
        </ul>
    </div>
</div>

CSS

ul li ul{padding-left:15px;}

JavaScript

$(function() {
	$('#general i .counter').text(' ');
	
	var generallen = $("#general-content input[name='wpmm[]']:checked").length;
	if(generallen>0){$("#general i .counter").text('('+generallen+')');}else{$("#general i .counter").text(' ');}
})

$("#general-content input:checkbox").on("change", function() {
	var len = $("#general-content input[name='wpmm[]']:checked").length;
	if(len>0){$("#general i .counter").text('('+len+')');}else{$("#general i .counter").text(' ');}
});


$(function() {
	$('.select_all').change(function() {
		var checkthis = $(this);
		var checkboxes = $(this).parent().next('ul').find("input[name='wpmm[]']");

		if(checkthis.is(':checked')) {
			checkboxes.attr('checked', true);
		} else {
			checkboxes.attr('checked', false);
		}
	});
})