Если вдруг не понял КСА
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<div class="greateparant">
<div class="parant">
<div class="child">
<div class="to-cart"></div>
</div>
</div>
<div class="parant">
<div class="child">
<div class="to-cart"></div>
</div>
</div>
<div class="parant">
<div class="child">
<div class="to-cart"></div>
</div>
</div>
</div>
<script>
[].forEach.call(document.querySelectorAll('.to-cart'), function(el) {
el.innerHTML = 'В корзину'
});
</script>
</body>
</html>