[jQuery] why is :first-child selecting sub elements?

[jQuery] why is :first-child selecting sub elements?


Hello all, I have a lay out like so
<div id="childtest_toprow">
        <div id="subtest_1">
            <div id="subtest_1_1"></div>
            <div id="subtest_1_2"></div>
        </div>
        </div>
        <div id="subtest_2">
        </div>
</div>
I want to select the first child of "childtest_toprow" which is
"subtest_1"
when i do
$("div[id ^= 'childtest_' ] :nth-child(1)").each(function() {
                    alert( $(this).attr("id") )
});
I get "subtest_1" AND "subest_1_1"
what am I doing wrong?
Thanks
ps: i'm using firefox 3 and IE 7