Dynamically calling multiple instances of a VI is often referred to as VI cloning...it's described in the following thread:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000A07D0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0&USEARCHCONTEXT_QUESTION_0=VI+cloning&USEARCHCONTEXT_QUESTION_S=0
Child panels is a new feature in LabVIEW 7; the container for the panel of the sub-VIs is found on Control palette -> containers - subPanel
If you are thinking of child windows though that can partially be achieved, read the following thread:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000F9530000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0&USEARCHCONTEXT_QUESTION_0=child+windows&USEARCHCONTEXT_QUES
TION_S=0
There's multiple threads on that issue, just search for child windows in this discussion group.