HWND ChildWindowFromPoint(HWND hParent, LPPOINT pPt)
 <MS-WINDOWS equivalent>

  This function determines which of a window's children occupies a
point. The top-most child which contains the point is returned.

Parameters
  hParent is the handle of the parent window.
  pPt is a far pointer to a POINT structure containing the 0-based row
      and column screen coordinates to test.

Returns
  The handle of the child window which contains that point, NULLHWND if none.