Need a way to close child window

Hi,
I have two windows open- parent & child. I need these windows to close for futher execution of my script
I have been facing some difficulty in closing the child window. I have tried using:

$handle=WinGetHandle("Child window title","")  -> (If I substitute the Title with 'parent window title', only parent window gets closed.)
WinClose($handle)
or
WinClose=("[ACTIVE]") ->( closes my commad prompts/ autoit editor)
or
WinKill=("[ACTIVE]") -> (kills my commad prompts/ autoit editor)

I tried adding AutoItSetOptions as well (WinTitleMatchMode/ WinSearchChildren/ WinDetectHiddenText) but in vain.

Looks like it's not detecting the child window at all. Would really appreciate some help here!

Thanks!