Ember: Access child function from parent component

components.child-component.js

import Ember from 'ember';

const {
  Component, set, get
} = Ember;

export default Component.extend({
  imageSource:'',
  didInsertElement() {
    get(this, 'setChildReference')(this);
  },
  doSomethingChildish() {
    set(this, 'imageSource', 'https://media.giphy.com/media/l1J9u3TZfpmeDLkD6/giphy.gif');
  }
});

components.parent-component.js

import Ember from 'ember';

const {
  Component, get, set
} = Ember;

export default Component.extend({
  actions: {
    setChildReference(childReference) {
      set(this, 'myChild', childReference);
    },
    callChildFunction() {
      get(this, 'myChild').doSomethingChildish();
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.parent-component-button {
  position: relative;
  left: 38vw;
}

.child-component-image {
  position: relative;
  left: 22vw;
  top: 10vh;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{parent-component}}
<br>
<br>

templates.components.child-component.hbs

<div class='child-component-image'>
  <img src={{imageSource}} alt='' height='300' width='300'>
</div>

templates.components.parent-component.hbs

<div class="parent-component-button">
  <button {{action 'callChildFunction'}}>Call child function</button>
</div>
<ChildComponent @setChildReference={{this.setChildReference}} />

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}