Preview:
var childMenu = document.querySelectorAll('.custom-menu-primary.visible-phone .hs-menu-wrapper > ul .hs-menu-item.hs-menu-depth-1.hs-item-has-children > a');
  Array.prototype.slice.call(childMenu).forEach(function (ele) {
    ele.insertAdjacentHTML('afterend', '<div class="child-trigger"></div>');
  });
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