How to get plus minus to update button text

I have been trying to get a plus minus button integrated into my number input. I have been able to update the field between the buttons with the new value however am trying to get that value to populate a second area (specifically a button) If I select the number input and click up or down arrows both the input and the button text are successfully updating, I am just stuck on mingling the two together.

How do I get the button to load the value of the number field after clicking the plus and minus buttons?

var adultModal = document.getElementById("adultModal");
var adultBtn = document.getElementById("guests");
var adultSpan = document.getElementsByClassName("adultClose")[0];

adultBtn.onclick = function() {
  adultModal.style.display = "block";
}

adultSpan.onclick = function() {
  adultModal.style.display = "none";
}

window.onclick = function(event) {
  if (event.target == adultModal) {
    adultModal.style.display = "none";
  }
}

// NUMBER FIELD PLUS / MINUS SCRIPT

function incrementValue(e) {
  e.preventDefault();
  var fieldName = $(e.target).data('field');
  var parent = $(e.target).closest('div');
  var currentVal = parseInt(parent.find('input[name=' + fieldName + ']').val(), 10);

  if (!isNaN(currentVal)) {
    parent.find('input[name=' + fieldName + ']').val(currentVal + 1);
  } else {
    parent.find('input[name=' + fieldName + ']').val(0);
  }

}

function decrementValue(e) {
  e.preventDefault();
  var fieldName = $(e.target).data('field');
  var parent = $(e.target).closest('div');
  var currentVal = parseInt(parent.find('input[name=' + fieldName + ']').val(), 10);

  if (!isNaN(currentVal) && currentVal > 0) {
    parent.find('input[name=' + fieldName + ']').val(currentVal - 1);
  } else {
    parent.find('input[name=' + fieldName + ']').val(0);
  }
}

$('.input-group').on('click', '.button-plus', function(e) {
  incrementValue(e);
});

$('.input-group').on('click', '.button-minus', function(e) {
  decrementValue(e);
});

function updateGuests() {
  let adultNumb = document.getElementById("adultQuantity");
  let produceAdult = document.getElementById('adultValue');
  produceAdult.innerHTML = adultNumb.value;

  let childNumb = document.getElementById("childQuantity");
  let produceChild = document.getElementById('childValue');
  produceChild.innerHTML = childNumb.value;
}

/* The Modal (background) */

.modal {
  display: none;
  /* Hidden by default */
  position: fixed;
  /* Stay in place */
  z-index: 1;
  /* Sit on top */
  padding-top: 100px;
  /* Location of the box */
  left: 0;
  top: 0;
  width: 100%;
  /* Full width */
  height: 100%;
  /* Full height */
  overflow: auto;
  /* Enable scroll if needed */
}


/* Modal Content */

.modal-content {
  background-color: #fefefe;
  margin: auto;
  padding: 5px 20px;
  border: 1px solid #888;
  width: 280px;
  position: relative;
}


/* The Close Button */

.adultClose,
.childClose {
  color: #aaaaaa;
  position: absolute;
  right: 5px;
  top: 0px;
  font-size: 22px;
  font-weight: bold;
  cursor: pointer;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}


/* INPUT NUMBER PLUS/MINUS BUTTONS */

input,
textarea {
  border: 1px solid #eeeeee;
  box-sizing: border-box;
  margin: 0;
  outline: none;
  padding: 10px;
}

input[type="button"] {
  -webkit-appearance: button;
  cursor: pointer;
}

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
  -webkit-appearance: none;
}

.input-group {
  clear: both;
  margin: 15px 0;
  position: relative;
}

.input-group input[type='button'] {
  background-color: #eeeeee;
  min-width: 38px;
  width: auto;
  transition: all 300ms ease;
}

.input-group .button-minus,
.input-group .button-plus {
  font-weight: bold;
  height: 38px;
  padding: 0;
  width: 38px;
  position: relative;
}

.input-group .quantity-field {
  position: relative;
  height: 38px;
  left: -6px;
  text-align: center;
  width: 62px;
  display: inline-block;
  font-size: 13px;
  margin: 0 0 5px;
  resize: vertical;
}

.button-plus {
  left: -13px;
}

input[type="number"] {
  -moz-appearance: textfield;
  -webkit-appearance: none;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<h3>Guests</h3>
<button id="guests" type="button" class="adults">
                <span class="bw-toggle__value"><span id="adultValue">2</span> Adults <span class="bw-divide">/</span> <span id="childValue">0</span> Children</span>
              </button>


<!-- Adult Modal -->
<div id="adultModal" class="modal">
  <!-- Modal content -->
  <div class="modal-content">
    <span class="adultClose">&times;</span>
    <div class="input-group">
      ADULTS
      <input type="button" value="-" class="button-minus" data-field="quantity">
      <input type="number" step="1" max="" value="2" name="quantity" class="quantity-field" id="adultQuantity" onchange="updateGuests()">
      <input type="button" value="+" class="button-plus" data-field="quantity">
    </div>
    <div class="input-group">
      CHILDREN
      <input type="button" value="-" class="button-minus" data-field="quantity">
      <input type="number" step="1" max="" value="0" name="quantity" class="quantity-field" id="childQuantity" onchange="updateGuests()">
      <input type="button" value="+" class="button-plus" data-field="quantity">
    </div>
  </div>
</div>

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