After months of searching, I finally found a post that outlines how to split a child window in an MFC MDI program.

Splitting Child Window in MFC MDI Program

For my purposes, this achievement is practically useless because I cannot find a way to pass text from one CRichEditView window to another.

Given two CRichEditView windows, CInputViewView and COutputView as child windows in an MFC MDI app, my goal is to capture text in the former and print that text in the later using a button click.

Using what appeared to me to be a logical way to proceed, I tried variations of the following code:
void CMainFrame::DoSomething()
	//MessageBox(_T("Like What ?"), _T("Do Something"));

	//CInputViewView * pin = (CInputViewView*) GetActiveView();
	CInputViewView * pin = (CInputViewView*)m_wndSplitter.GetPane(0,0);
	//CInputViewView* pInVV = (CInputViewView*) CChildFrame
	//long countChildren;
	//CChildFrame * pChildFrm = (CChildFrame*) get_accChildCount(&countChildren); //this->GetAccessibleChild(VARIANT varChild, IDispatch **ppdispChild);
	//pChildFrm->m_wndSplitter.GetPane(0, 1);
	//CString cs;
	//cs.Format(_T("countChildren = %d"), countChildren);

None of this works and even the attempt to access the pane results in an app crash in winsplit.cpp.
#ifdef _DEBUG
void CSplitterWnd::AssertValid() const
>	ASSERT(m_nMaxRows >= 1);
Please see attached demo.
Appreciate any help in accessing the panes from CMainFrame. Thanks