MDI Child windows and the OnIdle Message

Hello,
I'd like to ask how do I specify which child Window(s) I am talking to in MDI while
I am using the OnIdle message.
For example

Code:

---

void CApp::OnNewWinA()
{
POSITION curTemplatePos = GetFirstDocTemplatePosition();

        while(curTemplatePos != NULL)
        {
                CDocTemplate* curTemplate =
                        GetNextDocTemplate(curTemplatePos);
                CString str;
                curTemplate->GetDocString(str, CDocTemplate::docName);
                if(str == _T("Hello"))
                {
                        curTemplate->OpenDocumentFile(NULL);
                        return;
                }
        }
     
}
.....
// And same for other windows

BOOL CApp::OnIdle(LONG lCount)
{
        // TODO: Add your specialized code here and/or call the base class
        return CWinApp::OnIdle(lCount);
}

---

Just more background info, I am working on a project which involves DX9 and MDI
I need Windows to feed data to one of the child windows while its idle while the other one
is displaying tabular data. You can see from the above code snippet, I can refer to "Hello" as the child window I am communicating with while I am not sure what to do with "OnIdle" when I want to talk to "Hello". Any help would be greatly appreciated!

Thanks
Jack