:only-child Selector

only-child ( ) version added: 1.1.4

Description: Selects all elements that are the only child of their parent.

If the parent has other child elements, nothing is matched.

Examples:

Example: Change the text and add a border for each button that is the only child of its parent. 

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>css demo</title>

  <style>

  div {
    width: 100px;
    height: 80px;
    margin: 5px;
    float: left;
    background: #b9e;
  }

  </style>

  <script src="//code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
  

<div>
  <button>Sibling!</button>
  <button>Sibling!</button>
</div>

<div>
  <button>Sibling!</button>
</div>

<div>
  None
</div>

<div>
  <button>Sibling!</button>
  <button>Sibling!</button>
  <button>Sibling!</button>
</div>

<div>
  <button>Sibling!</button>
</div>

<script>

$( "div button:only-child" ).text( "Alone" ).css( "border", "2px blue solid" );

</script>

  
</body>
</html>

Demo: