How to write the selector?

How to write the selector?

Hi,
how can I select a list-item which is 3rd-Element and has a child span with a class?
  1. var paginationUl = jQuery('ul.pagination'),
  2.       paginationLi = jQuery('li', paginationUl),
  3.       firstLiNotCLass = jQuery('li:not([class])', paginationUl),
  4.       paginationStart = jQuery('.pagination-start', paginationUl),
  5.       paginationPrev = jQuery('.pagination-prev', paginationUl), 
  6.       paginationNext = jQuery('.pagination-next', paginationUl),
  7.       paginationEnd = jQuery('.pagination-end', paginationUl);

  8. if(jQuery(paginationLi).is(':nth-child(3)').children('span.active')) {
  9.       paginationStart.remove();
  10.       paginationPrev.remove();    
  11.     }


Here I got the error "Object true has no method children".