Question

How do I close all child popup windows which are already opened using jquery, after the user logs out?

Answer 1

As commented, your question is quite vague but maybe you should try to store the references to the popup windows e.g. in an array and close all those windows when logging out. The exact code depends on how you open the popups.

var openedPopups = new Array();
openedPopups.push($.openPopup(...));
...

(logging out)
for (var i=0, len=openedPopups.length; i<len; i++) {
  openedPopups[i].close();
}