Show child divs when checkboxes are checked

HTML

<div>
      <label for="set">Select question set:</label>
      <select type="select" name="set" id="set" required>
        <option value="">Select</option>
        <option value="set1" selected>One</option>
        <option value="set2">Two</option>
      </select>
    </div>
    
    <div id="set1" class="checkboxes">
      <input type="checkbox" name="set1-questions1" id="set1-questions1" checked>
      <label for="set1-questions1">Set 1 Questions 1</label>
      <br>
      <input type="checkbox" name="set1-questions2" id="set1-questions2">
      <label for="set1-questions2">Set 1 Questions 2</label>
      
      <div id="set1-questions1-qs" class="sub-questions">
        <h2>Set 1 Questions 1</h2>
        <label for="set1-questions1-q1">Set 1 Questions 1 Q1</label>
        <textarea name="set1-questions1-q1" id="set1-questions1-q1"></textarea>
        <label for="set1-questions1-q2">Set 1 Questions 1 Q2</label>
        <textarea name="set1-questions1-q2" id="set1-questions1-q2"></textarea>
      </div>
    
      <div id="set1-questions2-qs" class="sub-questions">
        <h2>Set 1 Questions 2</h2>
        <label for="set1-questions1-q2">Set 1 Questions 2 Q1</label>
        <textarea name="set1-questions2-q1" id="set1-questions2-q1"></textarea>
        <label for="set1-questions2-q2">Set 1 Questions 2 Q2</label>
        <textarea name="set1-questions2-q2" id="set1-questions2-q2"></textarea>
      </div>
    </div>
    
    <div id="set2" class="checkboxes">
      <input type="checkbox" name="set2-questions1" id="set2-questions1">
      <label for="set2-questions1">Set 2 Questions 1</label>
      <br>
      <input type="checkbox" name="set2-questions2" id="set2-questions2">
      <label for="set2-questions2">Set 2 Questions 2</label>
      
      <div id="set2-questions1-qs" class="sub-questions">
        <h2>Set 2 Questions 1</h2>
        <label for="set2-questions1-q1">Set 2 Questions 1 Q1</label>
        <textarea name="set2-questions1-q1"...

CSS

* {
  box-sizing:border-box;
}

body {
  font-family:sans-serif; 
  margin:1em auto;
  max-width:460px;
}

label {
  margin-bottom:1em;
}

textarea {
  margin-bottom:1em;
  min-width:100%;
}

ul {
  padding:0;
  list-style:none;
}

div {
  border-bottom:1px solid lightgrey;
  margin-bottom:1em;
  padding-bottom:1em;
}

.checkboxes,
.sub-questions {
  display:none;
}

JavaScript

// Show/Hide checkbox divs using select
$('#set').change(function(){
  $('.checkboxes').hide();
  $('#' + $(this).val()).show();
});

$('div.checkboxes input[type="checkbox"]').on('change', function() {
   $('#' + this.id + '-qs').toggle( this.checked ); 
});

// Sorted by triggering .change() on page load

/* E.g.
$('#set').change(function(){
    $('.checkboxes').hide();
    $('#' + $(this).val()).show();
}).change(); <- This bit!
*/