frame = new wxMDIParentFrame(Nothing, -1, "Parent Frame", wxPoint(-1, -1),wxSize(800, 600))
cFrame = new wxMDIChildFrame(frame, -1, "Child Frame", wxPoint(-1, -1), wxSize(788, 568))
frame.Show(1)

Sub onResize(event)
   cFrame.SetSize(frame.GetSizeWidth() - 12, frame.GetSizeHeight() - 32)
End Sub
Connect(frame, wxEVT_SIZE,"onResize") 