jquery: children() vs child selector ">"

I have a table that has a section similar to the following:

<tr>
    <td> <span class="myclass"></span>
    </td>
<tr>

my $(this) is set to the tr element and I'm trying to access the Span elements that have the "myclass" class set. The following seems to work:

if ($(this).children('td').children('span').is('.myclass')){
    alert('in here');
}

but when trying to use this:

if ($(this).children("td > span").is('.myclass')){

or this:

if ($(this).children("td span").is('.myclass')){

It does not. I thought that either of the above 2 would come up with similar results (albeit through different methods) but apparently not.

What am I missing here?

Thanks!