Check/Uncheck All CheckBoxes using Jquery

Hi,
How to check/uncheck checkboxes(Child) using a single(Parent) checkbox or vice-versa?
When i am using normal Html checkbox following code is working.
where Child and Parent are classes given to checkboxes.

// add multiple Check / Uncheck functionality
    $(".Parent").click(function () {
          $(".Child").attr("checked", this.checked);
    });

    // if all child checkbox are selected, check the Parent checkbox
    // and viceversa
    $(".Child").click(function(){

        if($(".Child").length == $(".Child:checked").length) {
            $(".Parent").attr("checked", "checked");
        } else {
            $(".Parent").removeAttr("checked");
        }
  });

But when i am using asp.net checkboxes this code is not working.
then i have modified the code as below.

// add multiple Check / Uncheck functionality
  //Parent class is having only one checkbox 
$(".Parent:first-child").click(
function() {
          $(".Child").find(":checkbox").attr("checked", this.checked);
    });

    // if all child checkbox are selected, check the Parent checkbox
    // and viceversa
    $(".Child").find(":checkbox").click(function(){

        if($(".Child").length == $(".Child:checked").length) {
            $(".Parent").find(":checkbox").attr("checked", "checked");
        } else {
            $(".Parent").find(":checkbox").removeAttr("checked");
        }
  });

Is this Because of Span Rendering Problem?
How to Solve this Problem?

Thanks in Advance.

Tags: jQuery, Checkbox, Selection