Select Second Child

Select second 2nd child div from within the parents div

You need to remove inline style from the second div tag

<div style="border-top: 1px solid #e5e5e5; width: 100%; line-height: 22px;">

It is overriding your css style.

For whatever reason if you want to keep the style, use !important although I highly DO NOT recommend this approach because it is very very bad practice but that's an option (however bad).

    .manufacturer_box div:nth-child(2) {
            border-top: 5px solid #e0e0e0 !important; 
     }

Select only the second child of an element with CSS

You can easily do with with nth-child:

#someID .text:nth-child(2) {
 background:red;   
}

Demo: http://jsfiddle.net/P6FKf/

CSS nth-child: what exactly does nth-child(1n) select

Xn essentially means every Xth child, where Xn+Y is every Xth child with an offset of Y.

1n is quite nonsensical, as it will just select every child (every 1th child, which essentially is just every child).

div:nth-child(1n)
{
  color: red;
}

<div>Hi</div>
<div>Hi</div>
<div>Hi</div>
<div>Hi</div>
<div>Hi</div>

Select the second child after some element

Looking at the two you say don't work, consider this structure:

h1+p+p::first-letter {
  color: red;
}

h1+p:nth-child(2)::first-letter {
  color: blue;
}

<body>
  <h1>H1</h1>
  <p>P1</p>
  <p>P2</p>
</body>

Get second child using jQuery

grab the second child:

$(t).children().eq(1);

or, grab the second child <td>:

$(t).children('td').eq(1);

See documentation for children and eq.

SCSS - nth-child(2) affects all descendants

If you look at how your SCSS actually gets compiled, you'll see it gets compiled to:

.my-class :nth-child(2) {
  padding-right: 15px;
  padding-left: 0;
}

Because CSS cascades (hence cascading style sheet), your :nth-child(2) will affect every second child.

I changed the padding to the left side, so it can be seen.

.my-class :nth-child(2) {

  padding-right: 0;

  padding-left: 15px;

}

<div class="my-class">

  <div>

    first

    <div>

      first child

    </div>

    <div>

      second child

      <div>

        first - second child

      </div>

      <div>

        second - second child

      </div>

    </div>

  </div>

  <div>

    second

  </div>

</div>