How can i add the numbers of checked checkbox to this jquery / js code

Please how can i add and display the numbers of checked checkboxes on this line of codes.

This is how the checkboxes works: It has a parent and child checkbox; when i check the parent checkbox (Checkall), it checks all (child checkboxes) and displays a div, when i each child checkbox (Single), it displays the div as well, and when i uncheck (Parent/Child) the div hides (jquery hide and show).

So, my problem here is that i want to add checkbox counter to the code. How to display the number count when i check the parent (Check all) and when i check each child (Single), and my div will still display (hide and show).

Please, help. Thanks a lot in advance. You can improve the codes (renovate) or rewrite. Here is the code below

$(document).ready(function() {
  $('#global').click(function() {
    $('.child').prop('checked', $(this).is(':checked'));

    if ($(this).is(':checked'))
      $('#mydiv').show();
    else
      $('#mydiv').hide();
  });

  $('.child').change(function() {
    var checkedLength = $('.child:checked').length;
    if (checkedLength > 0)
      $('#mydiv').show();
    else
      $('#mydiv').hide();
  });
});

<script src="http://ift.tt/1qRgvOJ"></script>
<div id="mydiv" style="display:none;">RESTORE | DELETE</div>

<input type="checkbox" id="global">
<br>
<input type="checkbox" class="child">
<input type="checkbox" class="child">
<input type="checkbox" class="child">
<input type="checkbox" class="child">
<input type="checkbox" class="child">
<input type="checkbox" class="child">
<input type="checkbox" class="child">

I'll be so glad :)