LinuxQuestions.org - GTK+ / Python spawn child window button press

I have been searching the web for 4 days now and I am unable to find an answer to my question. I've scoured the gnome website, but their GTK 3 documentation needs work. To me, it looks like a wall of text and is more of a command reference than actual useful documentation for someone who is learning. Anyways, end of rant.

I'm trying to write a simple program using GTK and Python. It should open a main window with a button. When the button, it should spawn a child window with a label. I cannot for the life of me get it to work. Could someone please help me figure out what I'm doing wrong??

Code:

#!/usr/bin/python

from gi.repository import Gtk



class MainWindow(Gtk.Window):

    def __init__(self):

        Gtk.Window.__init__(self, title="Main Window")

        self.set_default_size(500,300)

        self.set_border_width(30)

        test_button = Gtk.Button(label="Click Here")

        test_button.connect("clicked", self.on_button_click)

        grid = Gtk.Grid()

        grid.attach(test_button, 1, 1, 1, 1)

        self.add(grid)

    def on_button_click(self, widget):

        ButtonWindow()

        

class ButtonWindow(Gtk.Window):

    def __init__(self):

        Gtk.Window.__init__(self, title="Child Window")

        self.set_default_size(500,300)

        self.set_border_width(30)

        child_win.connect("destroy", self.destroy)

        grid = Gtk.Grid()

        test_label = Gtk.Label(label="Label on child window")

        grid.attach(test_label, 1, 1, 1, 1)



main_win = MainWindow()

child_win = ButtonWindow()

main_win.connect("delete-event", Gtk.main_quit)

main_win.show_all()

Gtk.main()

This code does not work. The main window spawns with a button, but clicking it does not spawn the child window. I have seen some programs that spawn a child window, but all of them close it with Gtk.main_quit, which then closes the entire program. Is GTK meant to only have 1 main window with no external windows?