I try to create custom child window that derive from `CWnd` inside `CFrameWnd` parent. The child window just rectangle with border style. Child create after parent create. it handle on `OnCreate` event. But the child window not appears. What's wrong here?

```
#include <afxwin.h>

class Index: public CWnd
{
  public:
    Index()
    {
      CWnd* parentWnd = AfxGetApp()->m_pMainWnd;

      Create(
        NULL, 
        NULL,
        WS_CHILD | WS_BORDER, 
        CRect(CPoint(0, 0), CSize(100, 100)),
        parentWnd, NULL, NULL);
    };
};

class MainFrame: public CFrameWnd
{
  public:
    MainFrame()
    {
      Create(
        NULL,
        "Parent and Child",
        WS_OVERLAPPEDWINDOW,
        CRect(CPoint(0, 0), CSize(640, 360))
      );
    };

  protected:
    afx_msg int OnCreate(LPCREATESTRUCT);
    DECLARE_MESSAGE_MAP()
};
BEGIN_MESSAGE_MAP(MainFrame, CFrameWnd)
  ON_WM_CREATE()
END_MESSAGE_MAP()

int MainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
  Index* index = new Index;
  index->ShowWindow(SW_NORMAL);

  return 0;
};

class Application: public CWinApp
{
  BOOL InitInstance()
  {
    m_pMainWnd = new MainFrame;
    m_pMainWnd->ShowWindow(SW_NORMAL);
    m_pMainWnd->UpdateWindow();

    return true;
  };    
};

Application app;

```