Thanks, Mithoric, here is the code to set child window title on the main menu item
Here I didn't create any menu item for child window, I think Windows could add them automatically to the menu item position "2" based on 0 is the 1st menu item.
CLIENTCREATESTRUCT clientcreate ;
hMenuMain = LoadMenu(hInstance, MAKEINTRESOURCE(IDR_MENUMAIN)); // Main menu
hMenuMainWindow = GetSubMenu(hMenuMain, 2); // set the menu item are displayed
clientcreate.hWindowMenu = hMenuMainWindow;
So here isn't any menu id created for child window.