Select nth child in jquery javascript
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select nth child like this
I want to select seconds child.


    $(this).prev().children[1].removeClass("necry").addClass("necry_er");


    <div class="reg_label">
    <div class="def"> Family </div>
    <div class="necry"> Necessary Field </div>
    <div class="clear"> </div>
    </div>
    <input id="ContentPlaceHolder1_LastName" class="reg_input" type="text" value="wef" name="ctl00$ContentPlaceHolder1$LastName">


I expact 

    <div class="necry**_er**"> Necessary Field </div>