To receive and process accelerator keys for its child windows, an MDI application must include the TranslateMDISysAccel function in its message loop. The loop must call TranslateMDISysAccel before calling the TranslateAccelerator or DispatchMessage function.
Accelerator keys on the window menu for an MDI child window are different from those for a non-MDI child window. In an MDI child window, the ALT+ - (minus) key combination opens the window menu, the CTRL+F4 key combination closes the active child window, and the CTRL+F6 key combination activates the next child window.