Unable to paint Child Windows Properly...

Question

I have a code for creating a simple Calculator, using Win32API :
https://code.sololearn.com/cwL1Kr251R5U/#cpp
On running the code, however, only the Label Box ( the window with ID = ID_LBL ) gets painted.
In my WM_CREATE message, I have used CreateWindow(), and the Numbers and Operator buttons are child classes for the main App window.
Then, why am I not able to see the other puttons being printed on the screen?
I tried replacing CreateWindow() with CreateWindowEx(), but I get the same output problem.
Another thing, is there a way to increase the font size of the text contained in these child windows?

Answer 1

@kurwius
That worked. Thank You. Silly me, I couldn't see such an error.