Selection td

<table id="test">
<tr id="1">
 <td>A</td><td>B</td>
</tr>
<tr id="2">
 <td>A2</td><td>B2</td>
</tr>
<tr id="3">
 <td>A3</td><td>B3</td>
</tr>
</table>

<script type="text/javascript">
//façon 1
var tbl = $("#test");
var tr = $(tbl).find('tr').first();
console.log('tr',tr);
var td = $(tr).find('td');
console.log('td',td);

//autre façon
var td2 = $("#test tr:first").find('td');
console.log('td2',td2);
</script>