Win32: C++: How do I re-focus on Parent Window after clicking in a child window?

In my Win32 CPP program, I have defined some Child Window to display various text strings using something like:

hnd_to_this_ch_window = CreateWindow( 
                        L"EDIT",L"Some initial text", WS_VISIBLE | WS_CHILD | ES_LEFT,  
                        position_of_this_window_X,              
                        position_of_this_window_Y,
                        TEXTOUT_DEFAULT_WIDTH,          
                        TEXTOUT_DEFAULT_HEIGHT, 
                        handle_to_my_parent_window, NULL,                        
                        hinstance_variable_used_by_create_window, 
                        NULL )

My problem is that if I click with my mouse to select the text in one of such child windows (to, say, copy it somewhere), the focus of the application goes to this child window and so any keypresses which used to be handled through my main windows CALLBACK (with case WM_KEYDOWN:) are now captured into the child window, where they appear as inputted characters. What magic function do I call to have the focus go back to the parent (so that my WM_KEYDOWN) can work again? I was hoping I could just click on the main Window's title bar and that would take it back to normal, but that isn't working (because, obviously, my program is lacking some extra logic).

Handle the WM_KILLFOCUS message in the window procedure of the window you want to focus, and restore the focus using the SetFocus function.

If you want to focus the window when it is clicked, handle the WM_LBUTTONDOWN message.

LRESULT CALLBACK MyWndProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
    // Restore the focus when it was lost.
    if (Msg == WM_KILLFOCUS) {
        SetFocus(hWnd);
        // Msg was handled, return zero.
        return 0;
    }
    // Or when the window is clicked.
    if (Msg == WM_LBUTTONDOWN) {
        SetFocus(hWnd);
        // Msg was handled, return zero.
        return 0;
    }
    return DefWindowProc(hWnd, Msg, wParam, lParam);
}