Kivy - Dispatching custom events to child widgets

I want to dispatch events from a LayoutDemoApp to a child widget. The goal is to have a websocket listener dispatch events, allowing any widget to listen to them (e.g. updating labels and so forth). I am probably misunderstanding how events works here and the Kivy examples. Is the register_event_type simply local to the LayoutDemoApp object, and this not possible?

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button

class MyButton(Button):
    def __init__(self, **kwargs):
        super(MyButton, self).__init__(**kwargs)
        
        self.bind(on_foo=self.on_foo)

    def on_foo(self, *args, **kwargs):
        print("MyButton.on_foo")


class LayoutDemoApp(App):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.register_event_type("on_foo")

    def build(self):
        root = BoxLayout(orientation='vertical')
        r1 = BoxLayout()
        
        button12 = MyButton(text='B1')
        button12.bind(on_press=self.on_bar)

        r1.add_widget(button12)
        root.add_widget(r1)
        return root

    def on_bar(self, *args, **kwargs):
        print("LayoutDemoApp.on_bar")
        self.dispatch("on_foo")
    
    def on_foo(self, *args, **kwargs):
        pass

if __name__ == '__main__':
    LayoutDemoApp().run()