Detecting a window within another window

I am trying to write an app using MFC which allows me to drag small dialogs around and drop them in static windows within a main dialog. The idea is, the small dialogs represent workers and the static windows represent work positions. The problem I am having is when I drop the second dialog in the same static window, it simply overlaps the first dialog so you can't tell there are two dialogs ( or three or four etc.).
I have been using this code to try and detect when the static has a dialog in it:

Code:

void CBoxes1Dlg::OnLButtonUp(UINT nFlags, CPoint point) 
{
	CRect rect;
	CWnd *pWnd1;
	CPoint pt;
	int y=0;

	CWnd *pWnd = ChildWindowFromPoint(point);
	if(pWnd!=NULL) {
		pWnd->GetWindowRect(rect);
		ScreenToClient (rect);
		pt.x=rect.left+5;
		pt.y=rect.top+5;
		pWnd1=pWnd->ChildWindowFromPoint(pt,CWP_ALL);
		
		if(pWnd1 == pWnd){
			// no dialog in this static box
		}else{
			// handles don't match so must be a dialog in the static already
		}
	}
	m_person->SetWindowPos(&CWnd::wndTop,(pt.x),(pt.y),0,0,SWP_NOSIZE|SWP_NOZORDER);
}

This doesn't work properly.....
Anyone see the problem or think of an easier way to do it.

Thanks
Zapper